Multilayer mounting mats and pollution control devices containing same

ABSTRACT

A multilayer mat for mounting a pollution control element in a pollution control device is provided. The mat comprises at least one first layer having at least one lateral edge requiring protection from exposure to (i) mechanical erosion forces generated by the impact of exhaust gases passing through a pollution control device, (ii) high temperatures associated with the exhaust gases, or both (i) and (ii). The mat also comprises at least one second layer having at least one lateral edge that is capable of protecting the at least one lateral edge of the first layer. The width of the first layer is less than the width of the second layer. The first and second layers are stacked one on top of the other such that the at least one lateral edge of the first layer is positioned between the opposite lateral edges of the second layer. The first layer has an exposed major surface.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage filing under 35 U.S.C. 371 ofPCT/US2006/039563, filed Oct. 10, 2006, which claims priority to U.S.Provisional Application No. 60/728,258, filed Oct. 19, 2005, thedisclosure of which is incorporated by reference in its/their entiretyherein.

FIELD OF THE INVENTION

The present invention relates to systems for mounting a pollutioncontrol element in a pollution control device (e.g., catalyticconverters, engine exhaust filters, etc), in particular, to mats formounting pollution control elements and, more particularly, suchmounting mats having multiple layers. The present invention also relatesto pollution control devices using such mounting mats and exhaustsystems that include such devices.

BACKGROUND

Pollution control devices are used to reduce atmospheric pollution fromthe exhaust systems of internal combustion engines such as, for example,those used in motor vehicles (e.g., automobiles, watercraft, aircraft,etc.), power generators and the like. Two typical types of suchpollution control devices are catalytic converters and exhaust systemfilters (e.g., diesel particulate filters) or traps. Catalyticconverters contain one or more catalyst support elements, which aretypically monolithic structures coated with desired catalyst material.The monolithic structure is typically made of ceramic, although metalshave also been used. The catalyst(s) oxidize carbon monoxide andhydrocarbons or reduce the oxides of nitrogen in exhaust gases. Exhaustsystem filters typically include a filter element in the form of ahoneycombed monolithic structure made from porous crystalline ceramicmaterials. In the current state-of-the-art construction of thesepollution control devices, their monolithic structure is mounted withina metal housing.

Protective packing or mounting materials are typically positionedbetween the pollution control element (e.g., monolithic structure) andthe metal housing to protect the pollution control element, for example,from road shock and vibration and to prevent exhaust gases from passingbetween the pollution control element and the metal housing. When aceramic monolithic structure is used, such mounting materials typicallyneed to compensate for the thermal expansion difference between themetal housing and the ceramic monolith. The process of mounting such amonolithic structure in a housing, with a mounting material, is referredto as “canning”. Such mounting processes have included inserting themonolith into the housing and injecting a paste into the gap between themonolith and the metal housing. Other mounting processes have alsoincluded wrapping a sheet material or mat around the monolith andinserting the wrapped monolith into the housing and welding the housingclosed. The compositions used to form conventional mounting materialshave included a variety of non-intumescent materials and intumescentmaterials.

The present invention is an improvement over such prior pollutioncontrol element mounting systems.

SUMMARY

The present invention can provide one or more of multilayer mountingmats for mounting a pollution control element in a pollution controldevice (e.g., catalytic converters, engine exhaust filters, etc.),pollution control devices including such multilayer mats, exhaustsystems including such pollution control devices, and methods for makingsuch mats, devices and exhaust systems.

In one aspect, a multilayer mat is provided for mounting a pollutioncontrol element in a pollution control device. The mat comprises atleast one first layer having an exposed major surface and a widthdefined by opposite lateral edges and at least one second layer having awidth defined by opposite lateral edges that is larger than the width ofthe first layer. At least one lateral edge of the first layer needsprotection from exposure to (i) mechanical erosion forces generated bythe impact of exhaust gases, passing through the pollution controldevice, that contact the at least one lateral edge of the first layer,(ii) high temperatures associated with such exhaust gases, or both (i)and (ii). At least one lateral edge of the second layer is sufficientlyresilient and durable to withstand exposure to such (i) mechanicalerosion forces generated by the impact of the exhaust gases, passingthrough the pollution control device, that contact the at least onelateral edge of the second layer, (ii) high temperatures associated withthe exhaust gases, or both (i) and (ii). The first layer and the secondlayer are stacked one on top of the other such that the at least onelateral edge of the first layer is positioned between the oppositelateral edges of the second layer and, when the multilayer mat ismounted in the pollution control device, the at least one lateral edgeof the second layer protects the at least one lateral edge of the firstlayer from exposure to exhaust gases passing through the pollutioncontrol device.

It can be desirable for the first layer to have an exposed majorsurface. In at least one embodiment, the exposed major surface of thefirst layer faces and may make direct contact with the housing of thepollution control device, such that the second layer is disposed betweenthe first layer and the pollution control element. In anotherembodiment, the first layer faces and may make contact with thepollution control element and at least part of the second layer isdisposed between the housing and the first layer.

Both lateral edges of the first layer may require protection fromexposure to at least one of mechanical erosion forces generated by theimpact of the exhaust gases and high temperatures associated with theexhaust gases.

Both lateral edges of the first layer may be positioned between theopposite lateral edges of the second layer such that, when themultilayer mat is mounted in the pollution control device, both lateraledges of the first layer are protected from exposure to exhaust gasespassing through the pollution control device.

The at least one lateral edge of the first layer may require protectionfrom exposure to the maximum operating temperature of the pollutioncontrol device and the at least one lateral edge of the second layer ispreferably sufficiently resilient and durable to withstand exposure tothe maximum operating temperatures of the pollution control device.

The first and second layers may be joined together.

The at least one first layer may comprise at least two first layers, theat least one second layer may comprise at least two second layers, orboth the at least one first layer may comprise at least two first layersand the at least one second layer may comprise at least two secondlayers.

In one embodiment, the at least one first layer and the at least onesecond layer each comprise a non-intumescent layer. In anotherembodiment, the at least one first layer and the at least one secondlayer each comprise an intumescent layer. In a further embodiment, theat least one first layer comprises a non-intumescent layer, and the atleast one second layer comprises an intumescent layer. In still afurther embodiment, the at least one first layer is an intumescentlayer, and the at least one second layer is a non-intumescent layer.

The width of each of the at least two first layers may be different, thewidth of each of the at least two second layers may be different, andthe width of each first layer may be less than the width of each secondlayer.

The at least one first layer and the at least one second layer may bedisposed relative to one another such that both lateral edges of the atleast one first layer are positioned within the lateral edges of the atleast one second layer.

The at least one first layer and the at least one second layer may bedisposed relative to one another such that one of the lateral edges ofthe at least one first layer is in-line with one of the lateral edges ofthe at least one second layer, and only the other lateral edge of the atleast one first layer lies within the lateral edges of the at least onesecond layer.

The multilayer mat may further comprise a strip of one or more layerspositioned alongside one lateral edge of the at least one first layer,wherein the width of the strip is narrower than the width of the atleast one first layer.

The combined widths of the strip and the first layer may together besubstantially equal to the width of the second layer.

The multilayer mat may further comprise another strip of one or morelayers, with one strip being disposed alongside each lateral edge of theat least one first layer, wherein the width of each strip is narrowerthan the width of the at least one first layer. The combined widths ofboth strips and the first layer may together be substantially equal tothe width of the second layer.

Each strip and the at least one first layer may be substantiallyco-planar. Further, each strip may have a length that is substantiallyequal to the length of the at least one first layer.

Each strip may be more resilient than the second layer. Alternatively,the second layer may be more resilient than any strip.

In accordance with a second aspect, a pollution control device isprovided comprising a housing having an inner wall, a pollution controlelement disposed in the housing so as to form a gap therebetween, and amultilayer mat, such as one of the multilayer mats discussed above. Themat is disposed in the gap so as to mount the pollution control elementin the housing.

A portion of the inner wall of the housing can be adapted to define arecess, and the mat can be positioned so that at least a portion of onlythe first layer is received within the recess.

A portion of the inner wall of the housing may define a recess. The matmay be positioned so that at least a portion of the first layer isreceived within the recess, and neither lateral edge of the first layeris exposed to exhaust gases passing through the pollution controldevice.

A portion of the inner wall of the housing may define a recess. The matmay be positioned so that the first layer is received within the recess,and one lateral edge of the first layer is exposed to exhaust gasespassing through the pollution control device.

A portion of the inner wall of the housing defines a recess. The mat maybe positioned so that the first layer is received within the recess andnot exposed to exhaust gases passing through the pollution controldevice, and one strip is exposed to exhaust gases passing through thepollution control device.

The second layer may be positioned adjacent the pollution controlelement.

The first layer may be positioned adjacent the inner wall of thehousing.

At least one of the lateral edges of the first layer may besubstantially sealed from exposure to exhaust gases passing through thepollution control device.

The pollution control device may comprise a catalytic converter or anexhaust system filter.

In accordance with a third aspect, an exhaust system for an internalcombustion engine is provided and comprises a pollution control deviceconstructed in accordance with the principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional view of a mat constructed inaccordance with a first embodiment;

FIG. 2 is a schematic top view of the mat illustrated in FIG. 1;

FIG. 3 is a perspective exploded view of a catalytic converter includingthe mat illustrated in FIG. 1;

FIG. 4 is a schematic cross sectional view of a catalytic converterincluding the mat of FIG. 1;

FIG. 4A is a schematic cross sectional view of a catalytic converterincluding a metal housing with a recess and multilayer mat formed inaccordance with a third embodiment;

FIG. 5 is a schematic cross sectional view of a catalytic converterincluding a multilayer mat formed in accordance with a fourthembodiment;

FIG. 5A is a schematic cross sectional view of a catalytic converterincluding a multilayer mat formed in accordance with a fifth embodiment;

FIG. 6 is a schematic cross sectional view of a multilayer mat formed inaccordance with a sixth embodiment;

FIG. 7 is a schematic cross sectional view of a catalytic converterincluding the mat of FIG. 6;

FIG. 8 is a schematic cross sectional view of a multilayer mat formed inaccordance with a seventh embodiment;

FIG. 9 is a schematic cross sectional view of a catalytic converterincluding the mat of FIG. 8;

FIG. 10 is a schematic cross sectional view of a catalytic converterincluding a multilayer mat formed in accordance with an eighthembodiment;

FIG. 11 is a schematic cross sectional view of a multilayer mat formedin accordance with a ninth embodiment;

FIG. 12 is a schematic cross sectional view of a catalytic converterincluding the mat of FIG. 11; and

FIG. 13 is a schematic cross sectional view of a catalytic converterincluding a multilayer mat formed in accordance with a secondembodiment.

DETAILED DESCRIPTION

A multilayer mat 10, constructed in accordance with a first embodiment,is illustrated in FIGS. 1 and 2. As will be discussed below, the mat 10may be used for mounting a pollution control element in a pollutioncontrol device. The mat 10 comprises a non-intumescent layer 12comprising suitable ceramic or other inorganic fibers and has a width W₁defined by opposite lateral edges 14 and 16 and a length L₁. The mat 10further comprises an intumescent layer 20 comprising intumescentmaterial and has a width W₂ defined by opposite lateral edges 22 and 24and a length L₂. In the illustrated embodiment, the width W₂ of theintumescent layer 20 is less than the width W₁ of the non-intumescentlayer 12. Further, the intumescent layer 20 is positioned relative tothe non-intumescent layer such that its two lateral edges 22 and 24 arepositioned within the two lateral edges 14 and 16 of the non-intumescentlayer 12. As illustrated in FIG. 1, the intumescent layer 20 comprisesan exposed major surface 20A having an area defined by its width W₂times its length L₂. The major surface 20A also defines an outermostlayer of the mat 10.

As noted above, the mat 10 may be used to mount a pollution controlelement in a pollution control device. For example, the mat 10 may beused to mount a pollution control element comprising a catalyst supportelement 40, which, in the illustrated embodiment, comprises a monolithicstructure coated with a catalyst material in a metal housing 50, seeFIGS. 3 and 4. The catalyst support element 40, mat 10 and metal housing50 define a catalytic converter 60, see FIG. 3. The metal housing 50 hasan inlet 52 and an outlet 54 through which exhaust gases flow into andout of the catalytic converter 60. The metal housing 50 can be formedfrom one or more metals, metal alloys, or intermediate compositions,such as stainless steel or austenitic steel.

Preferably, a substantially resilient non-intumescent layer 12 isselected such that once the mat 10 and the catalyst support element 40have been mounted within the metal housing 50, outer portions 18A and18B of the non-intumescent layer 12 fill the gap G, in at least the sealareas A_(S), between an inner wall of the housing 50 and the supportelement 40, see FIG. 4, so as to seal the gap G and protect the lateraledges 22 and 24 of the intumescent layer 20. The outer portions 18A and18B resiliently fill the gap G, when at ambient temperature or a highoperational temperature. In other words, at least the outer portions 18Aand 18B of the non-intumescent layer 12 are resilient enough to exert asufficient pressure to seal the gap G and protect the intumescent layer20, whether the gap G is at its smallest (i.e., at ambient temperature)or biggest (i.e., at the highest operating temperature). It is desirablefor at least these outer portions 18A and 18B to also be durable enoughto survive cycling of the gap G between its smallest and biggest overthe desired life of the pollution control device. It can be preferablefor the entire non-intumescent layer 12 to exhibit this degree ofresilience and durability.

Hence, the intumescent layer lateral edges 22 and 24 are substantiallysealed from exposure to exhaust gases, especially high temperatureexhaust gases, flowing through the catalytic converter 60. When thecatalytic converter 60 experiences high operational temperatures,exposure of the intumescent layer 20 to high temperature exhaust gasescan damage the intumescent material in (i.e., the intumescentcharacteristics of) the layer 20, especially along exposed surfaces.Such damage can exacerbate the erosion of the layer 20 with increasedexposure to the flowing exhaust gases. For example, vermiculite, whichcan be used to form part of some intumescent layers 20, can loose itsintumescent characteristics when exposed to temperatures in excess ofabout 750° C. Hence, if the intumescent layer 20 is exposed to suchdamaging high temperatures, damaged portions of the layer 20 may beunable to sufficiently expand and fill the gap G with enough of amounting force to prevent erosion of the layer 20. Even if exposed toexhaust gases at below such damaging high temperatures, the exhaustgases can still cause erosion of the layer 20. By insulating orshielding the intumescent layer 20 from exposure to exhaust gases viathe outer portions 18A and 18B of the non-intumescent layer 12 and alsoinsulating the layer 20 from high temperatures radiated by the element40 via the non-intumescent layer 12, the intumescent layer 20 is,therefore, less likely to lose its intumescent capability to expand asthe metal housing 50 expands due to increased temperatures during use ofthe catalytic converter 60. Because some intumescent materials are lessexpensive than some non-intumescent materials, this embodiment canprovide a mat formed at a lower cost than mats formed primarily ofnon-intumescent material(s) yet still function in an adequate manner tomaintain a catalyst support element 40 tightly supported within acatalytic converter metal housing 50 during use of the catalyticconverter 60.

In addition to being left unsecured to each other, the intumescent layer20 can be joined to the non-intumescent layer 12 such as, for example,by using adhesive, needle bonding, stitching, tape banding, tagattachment or co-forming, or adjacent portions of the material definingthe layers 12 and 20 may be mechanically interconnected with oneanother.

Although FIGS. 1 and 2 illustrate a mat 10 comprising only two layers,one or more additional intumescent layers may be provided and/or one ormore additional non-intumescent layers may be provided. The differentintumescent layers may have different properties, such as differentexpansion, compression and/or erosion properties. The differentnon-intumescent layers may also have different properties, such asdifferent resiliency values and/or maximum temperature limitations. Anadditional example of a multilayer mat constructed in accordance withthe first embodiment includes layers arranged in the following order:intumescent/non-intumescent/intumescent/non-intumescent.

As used herein, the term “intumescent layer” refers to a layer thatexpands intumescently, other than only as a result of its coefficient ofthermal expansion, for example by the inclusion of intumescent expandingmaterials such as vermiculite, expandable graphite, micas, and likematerials. Typically, such layers need to be protected from erosioncaused by exposure to hot exhaust gases.

As used herein, the term “non-intumescent layer” refers to a layer thatexhibits very little or no intumescent expansion. That is, most or allof any expansion of the layer from heat exposure is the result of itscoefficient of thermal expansion. Examples of non-intumescent materialsinclude, without limitation, ceramic and other inorganic fibers.

Specific examples of substantially resilient non-intumescent materialsfrom which the non-intumescent layer 12 may be formed include materialscommercially available from 3M Company (St. Paul, Minn.) under the tradedesignation “INTERAM 1000HT,” “INTERAM 1100HT,” “INTERAM 1101HT,”“INTERAM 1200NC,” “INTERAM 1500HT,” “INTERAM 1535HT,” “INTERAM 1550HT,”“INTERAM 1600HT,” and “INTERAM 1600HTE.” Specific example intumescentmaterials from which the intumescent layer 20 may be formed includematerials commercially available from 3M Company (St. Paul, Minn.) underthe trade designation “INTERAM 100,” “INTERAM 200,” “INTERAM 550,”“INTERAM 2000LT,” “INTERAM X-D,” “INTERAM 1M,” “INTERAM 1S,” “INTERAM570NC,” and “INTERAM 600NC.”

For a catalytic converter 60 having a mat 10 comprising a resilientnon-intumescent layer 12 formed from “INTERAM 1100HT” or “INTERAM1535HT” and an intumescent layer 20 formed from “INTERAM 550” or“INTERAM 1M,” and a gap G between an inner wall of the housing 50 andthe support element 40, see FIG. 4, equal to about 3 mm, it is believedthat the resilient non-intumescent layer 12 can have a minimum basisweight of about 750 g/m², the intumescent layer 20 can have a minimumbasis weight of about 675 g/m², and wherein the density of the combinednon-intumescent layer 12 and intumescent layer 20 in a mount area A_(M)of the gap G is equal to about 0.475 g/cc and the density of outerportions 18A, 18B of the non-intumescent layer 12 in the seal areasA_(S) of the gap G is equal to about 0.25 g/cc. For a gap equal to about4 mm, it is believed that the resilient non-intumescent layer 12 canhave a minimum basis weight of about 1000 g/m², the intumescent layer 20can have a minimum basis weight of about 900 g/m², and wherein thedensity of the combined non-intumescent layer 12 and intumescent layer20 in the mount area A_(M) of the gap G is equal to about 0.475 g/cc andthe density of outer portions 18A, 18B of the non-intumescent layer 12in the seal areas A_(S) of the gap G is equal to about 0.25 g/cc. For agap equal to about 6 mm, it is believed that the resilientnon-intumescent layer 12 can have a minimum basis weight of about 1500g/m², the intumescent layer 20 can have a minimum basis weight of about1350 g/m², and wherein the density of the combined non-intumescent layer12 and intumescent layer 20 in the mount area A_(M) of the gap G isequal to about 0.475 g/cc and the density of outer portions 18A, 18B ofthe non-intumescent layer 12 in the seal areas A_(S) of the gap G isequal to about 0.25 g/cc. For a gap equal to about 8 mm, it is believedthat the resilient non-intumescent layer 12 can have a minimum basisweight of about 2000 g/m², the intumescent layer 20 can have a minimumbasis weight of about 1800 g/m², and wherein the density of the combinednon-intumescent layer 12 and intumescent layer 20 in the mount areaA_(M) of the gap G is equal to about 0.475 g/cc and the density of outerportions 18A, 18B of the non-intumescent layer 12 in the seal areasA_(S) of the gap G is equal to about 0.25 g/cc. In each of the propheticexamples set out above, in the mount area A_(M) of the gap G where boththe intumescent and non-intumescent layers 20 and 12 are positioned, itis believed that the intumescent layer 20 will fill approximately 25% ofthe gap, while the non-intumescent layer 12 will fill about 75% of thegap. It is believed that the outer portions 18A, 18B of thenon-intumescent layer 12 in the seal areas A_(S) of the gap G, ifprovided at a minimum density of about 0.25 g/cc, will function in anacceptable manner to insulating the intumescent layer 20 from exposureto exhaust gases.

It is contemplated that the mat 10 illustrated in FIGS. 1-2 may also beused in low temperature applications. Such a multilayer mat 710, inaccordance with a second embodiment, is illustrated in FIG. 13. The mat710 comprises a non-intumescent layer 712 comprising ceramic fibers andhas a width W₁ defined by opposite lateral edges 714 and 716 and alength L₁. The mat 710 further comprises an intumescent layer 720comprising intumescent material and has a width W₂ defined by oppositelateral edges 722 and 724 and a length L₂. In the illustratedembodiment, the width W₂ of the intumescent layer 720 is less than thewidth W₁ of the non-intumescent layer 712. Further, the intumescentlayer 720 is positioned relative to the non-intumescent layer such thatits two lateral edges 722 and 724 are positioned within the two lateraledges 714 and 716 of the non-intumescent layer 712. As illustrated inFIG. 13, the intumescent layer 720 comprises an exposed major surface720A having an area defined by its width W₂ times its length L₂. Themajor surface 720A also defines an innermost layer of the mat 710.

As illustrated in FIG. 13, the mat 710 is positioned so as to mount apollution control element, such as a catalyst support element 40, in ametal housing 50. The catalyst support element 40, mat 710 and metalhousing 50 define a catalytic converter 760.

Preferably, a substantially resilient non-intumescent layer 712 isselected such that once the mat 710 and the catalyst support element 40have been mounted within the metal housing 50, outer portions 718A and718B of the non-intumescent layer 712 sufficiently expand in the sealareas A_(S) of a gap G, between an inner wall of the housing 50 and thesupport element 40, so as to seal the lateral edges 722 and 724 of theintumescent layer 720, as the gap G expands with increasingtemperatures. Thus, the outer portions 718A and 718B continue to fillthe gap G when at ambient temperature or a high operational temperature.In other words, at least the outer portions 718A and 718B of thenon-intumescent layer 712 are resilient enough to exert a sufficientpressure to seal the gap G and protect the intumescent layer 720,whether the gap G is at its smallest (i.e., at ambient temperature) orbiggest (i.e., at the highest operating temperature). It is desirablefor at least these outer portions 718A and 718B to also be durableenough to survive cycling of the gap G between its smallest and biggestover the desired life of the pollution control device. It can bepreferable for the entire non-intumescent layer 712 to exhibit thisdegree of resilience and durability. Hence, the intumescent layerlateral edges 722 and 724 are substantially sealed from exposure to highor low temperature exhaust gases flowing through the catalytic converter760.

In the pollution control device 60 of FIGS. 3-4, the intumescent layer20 forms an outermost layer of the mat 10. Hence, the mat 10 isadvantageous for use in mounting a pollution control element in apollution control device that operates at high temperatures such thatthe intumescent layer 20 faces and makes contact with the pollutioncontrol device metal housing. As a result, energy in the form of heat istransferred efficiently from the intumescent layer 20 to the metalhousing so as to help protect the intumescent layer 20 from overheating,when exposed to high temperatures. The intumescent layer 20 is alsoprotected from high temperatures radiated by the element 40 via thenon-intumescent layer 12. In the pollution control device 760 of FIG.13, the intumescent layer 720 forms an innermost layer of the mat 710.Hence, the mat 710 is advantageous for use in mounting a pollutioncontrol element, such as element 40, in a pollution control device thatoperates at relatively low temperatures such that the intumescent layer720 faces and makes contact with the pollution control element so thatthe intumescent layer 720 receives sufficient energy in the form of heatto cause the layer 720 to intumescently expand to the degree desired.

In a third embodiment, where like reference numerals indicate likeelements, a mat 10A is used to support and mount a support element 40 ina metal housing 150 so as to define a catalytic converter 180, see FIG.4A. The metal housing 150 is rolled or otherwise formed so as to includea recess 150A, which, in the illustrated embodiment, extends about theentirety of the housing 150. By forming the recess 150A within thehousing 150, the stiffness of the housing is enhanced. The housingrecess 150A is shaped in X and Z directions so as to define a pocketsized to receive the intumescent layer 20 and shaped to substantiallyshield the intumescent layer lateral edges 22 and 24 from exhaust gasespassing through the catalytic converter 180. Because the gap GA does notaccommodate the thickness of both the intumescent layer 20 and thenon-intumescent layer 13, the layer 13 does not need to expand as muchto sufficiently fill the gap GA, as the gap increases with increasingtemperature. As a result, the non-intumescent layer 13 in the FIG. 4Aembodiment may be formed from a material having less resiliency than thematerial used to form the non-intumescent layer 12 in the FIG. 4embodiment. For example, the non-intumescent layer 13 may be formed froma material commercially available from 3M Company (St. Paul, Minn.)under the trade designation “INTERAM 900HT.”

A multilayer mat 70 constructed in accordance with a fourth embodimentis illustrated in FIG. 5, where like reference numerals indicate likeelements. The mat 70 comprises a non-intumescent layer 12 comprisingceramic fibers and has a width W₁ defined by opposite lateral edges 14and 16 and a length L₁. The mat 10 further comprises an intumescentlayer 72 comprising intumescent material and has a width W₃ defined byopposite lateral edges 74 and 76 and a length substantially equal tolength L₁ of the non-intumescent layer 12. In the illustratedembodiment, the width W₃ of the intumescent layer 72 is less than thewidth W₁ of the non-intumescent layer 12. Further, the intumescent layer72 is positioned relative to the non-intumescent layer 12 such thatlateral edge 74 is positioned within the two lateral edges 14 and 16 ofthe non-intumescent layer 12 and lateral edge 76 is substantiallyin-line with lateral edge 16.

In FIG. 5, the mat 70 is shown provided within a metal housing 50 so asto support and maintain a catalyst support element 40 within the housing50. The mat 70, housing 50 and support element 40 define a catalyticconverter 80. Exhaust gases pass through the catalytic converter 80 fromleft to right as viewed in FIG. 5.

Preferably, a substantially resilient non-intumescent layer 12 isselected for use in the catalytic converter 80 such that once the mat 70and the catalyst support element 40 are positioned within the metalhousing 50, an outer or exposed portion 18A of the non-intumescent layer12 fills the gap G so as to seal and protect the lateral edge 74 of theintumescent layer 72. Hence, the intumescent layer lateral edge 74 issubstantially sealed from direct exposure to high temperature exhaustgases flowing through the catalytic converter 80. It is noted that inthe FIG. 5 embodiment, the other lateral edge 76 of the intumescentlayer 72 is not sealed by the non-intumescent layer 12. However, becausethe lateral edge 76 is not directly exposed to the incoming flow of theexhaust gases, loss of intumescent material from lateral edge 76 may beminimal or insubstantial for some catalytic converter designs such as,for example, substantially round housing designs.

The non-intumescent layer 12 may be formed from one of the samematerials, set out above, from which the layer 12 in the FIG. 1embodiment is formed. The intumescent layer 72 may be formed from one ofthe same intumescent materials, set out above, from which the layer 20in the FIG. 1 embodiment is formed.

In the FIG. 5 embodiment, the intumescent layer 72 is shown positionedadjacent to the catalytic converter metal housing 50. However, for someapplications, such as low temperature applications, the intumescentlayer 72 may be positioned adjacent to the catalyst support element 40.

In a fifth embodiment, where like reference numerals indicate likeelements, a mat 170 is used to support and mount a support element 40 ina metal housing 250 so as to define a catalytic converter 280, see FIG.5A. The metal housing 250 is formed so as to include a recess 250A,which, in the illustrated embodiment, extends about the entirety of thehousing 250. The housing recess 250A is shaped in X and Z directions soas to receive the intumescent layer 72 and substantially shield theintumescent layer lateral edge 74 from exhaust gases passing through thecatalytic converter 280. Hence, the intumescent layer lateral edge 74 issubstantially sealed from direct exposure to incoming high temperatureexhaust gases flowing through the catalytic converter 280. It is notedthat in the FIG. 5A embodiment, the lateral edge 76 of the intumescentlayer 72 is not sealed by the non-intumescent layer 13. However, becausethe lateral edge 76 is not positioned in the incoming path of theexhaust gases, loss of intumescent material from lateral edge 76 may beminimal for some catalytic converter housing designs. It is also notedthat because the non-intumescent layer 13 does not need to expand assubstantially in the Z direction to shield the lateral edges 74 and 76of the intumescent layer 72 from exhaust gases, the non-intumescentlayer 13 in the FIG. 5A embodiment may be formed from a material havingless resiliency than the material used to form the non-intumescent layer12 in the FIG. 5 embodiment. For example, the non-intumescent layer 13may be formed from the same non-intumescent material, set out above,from which the non-intumescent layer 13 in the FIG. 4A embodiment isformed.

A multilayer mat 90 constructed in accordance with a sixth embodiment isillustrated in FIG. 6, where like reference numerals indicate likeelements. The mat 90 comprises an inner non-intumescent layer 13comprising ceramic fibers and has a width W₁ defined by opposite lateraledges 14 and 16 and a length L₁. The mat 10 further comprises anintumescent layer 20 comprising intumescent material and has a width W₂defined by opposite lateral edges 22 and 24 and a length substantiallyequal to length L₁ of the non-intumescent layer 13. In the illustratedembodiment, the width W₂ of the intumescent layer 20 is less than thewidth W₁ of the non-intumescent layer 13. Further, the intumescent layer20 is positioned relative to the non-intumescent layer 13 such that thelateral edges 22 and 24 are positioned within the two lateral edges 14and 16 of the non-intumescent layer 13.

The multilayer mat 90 further comprises first and second strips 92 and94, respectively, of non-intumescent material. The first non-intumescentstrip 92 is positioned over a first outer portion 18A of thenon-intumescent layer 13 and the second non-intumescent strip 94 ispositioned over a second outer portion 18B of the non-intumescent layer13. The first non-intumescent strip 92 has a width W₄ and a lengthsubstantially equal to the lengths of the inner non-intumescent layer 13and the intumescent layer 20. The second non-intumescent strip 94 has awidth W₅ and a length substantially equal to the lengths of the innernon-intumescent layer 13 and the intumescent layer 20. In theillustrated embodiment, the summation of the width W₂ of the intumescentlayer 20, the width W₄ of the first non-intumescent strip 92 and thewidth W₅ of the second non-intumescent strip 94 is substantially equalto the width W₁ of the inner non-intumescent layer 13.

In FIG. 7, the mat 90 is shown provided within a metal housing 50 so asto support and maintain a catalyst support element 40 within the housing50. The mat 90, housing 50 and support element 40 define a catalyticconverter 380.

Preferably, the non-intumescent strips 92 and 94 are formed from asubstantially resilient non-intumescent material for use in thecatalytic converter 380 such that once the mat 90 and the catalystsupport element 40 are positioned within the metal housing 50, thestrips 92 and 94 sufficiently expand in seal areas A_(S) of a gap G,between an inner wall of the housing 50 and the support element 40, seeFIG. 7, so as to seal the lateral edges 22 and 24 of the intumescentlayer 20, as the gap G expands with increasing temperatures. In otherwords, at least the strips 92 and 94 are resilient enough to exert asufficient pressure to seal the gap G and protect the lateral edges 22and 24 of the intumescent layer, whether the gap G is at its smallest(i.e., at ambient temperature) or biggest (i.e., at the highestoperating temperature). It is desirable for at least these strips 92 and94 to also be durable enough to survive cycling of the gap G between itssmallest and biggest over the desired life of the pollution controldevice. It can be preferable for the non-intumescent layer 13 to alsoexhibit this degree of resilience and durability. Hence, the intumescentlayer lateral edges 22 and 24 are substantially sealed from exposure tohigh temperature exhaust gases flowing through the catalytic converter380. It is noted that the inner non-intumescent layer 13 may be formedfrom a material which is less resilient than the non-intumescent strips92 and 94. Typically, a less resilient non-intumescent material is lessexpensive than a more resilient non-intumescent material. For example,the non-intumescent strips 92 and 94 may be formed from one of the samematerials, set out above, from which the layer 12 in the FIG. 1embodiment is formed. The intumescent layer 72 may be formed from one ofthe same intumescent materials, set out above, from which theintumescent layer 20 in the FIG. 1 embodiment is formed. Thenon-intumescent layer 13 may be formed from the same non-intumescentmaterial, set out above, from which the non-intumescent layer 13 in theFIG. 4A embodiment is formed.

It is also contemplated that the non-intumescent strips 92 and 94 may beformed from a less resilient non-intumescent material while thenon-intumescent layer 13 may be formed from a substantially resilientnon-intumescent material. In this embodiment, once the mat and thecatalyst support element 40 are positioned within the metal housing 50,the non-intumescent layer 13 provides the resiliency needed to sealareas A_(S) of the gap G between the inner wall of the housing 50 andthe support element 40 so as to protect the lateral edges 22 and 24 ofthe intumescent layer 20 during low and high operating temperatures ofthe pollution control device.

For a catalytic converter 380 having a mat 90 comprising anon-intumescent layer 13 formed from “INTERAM 900HT,” an intumescentlayer 20 formed from “INTERAM 100” or “INTERAM 550” and non-intumescentstrips 92, 94 formed from “INTERAM 1100HT,” “INTERAM 1101HT,” “INTERAM1535HT,” or “INTERAM 1600HTE” and having a gap G between an inner wallof the housing 50 and the support element 40, see FIG. 7, equal to about3 mm, it is believed that the non-intumescent layer 13 may have aminimum basis weight of about 750 g/m², the intumescent layer 20 mayhave a minimum basis weight of about 1550 g/m², and each non-intumescentstrip 92 and 94 may have a minimum basis weight of about 450 g/m² andwherein the compressed density of the combined non-intumescent layer 13and intumescent layer 20 in a mount area A_(M) of the gap G is about0.77 g/cc and the compressed density of the combined non-intumescentlayer 13 and a strip 92 or 94 in each seal area A_(S) of the gap G isequal to about 0.40 g/cc. For a gap equal to about 4 mm, it is believedthat the non-intumescent layer 13 may have a minimum basis weight ofabout 1020 g/m², the intumescent layer 20 may have a minimum basisweight of about 2100 g/m², and each non-intumescent strip 92 and 94 mayhave a minimum basis weight of about 600 g/m² and wherein the compresseddensity of the combined non-intumescent layer 13 and intumescent layer20 in the mount area A_(M) of the gap G is about 0.77 g/cc and thecompressed density of the combined non-intumescent layer 13 and a strip92 or 94 in each seal area A_(S) of the gap G is equal to about 0.40g/cc. For a gap equal to about 6 mm, it is believed that thenon-intumescent layer 13 may have a minimum basis weight of about 1435g/m², the intumescent layer 20 may have a minimum basis weight of about3100 g/m², and each non-intumescent strip 92 and 94 may have a minimumbasis weight of about 900 g/m² and wherein the compressed density of thecombined non-intumescent layer 13 and intumescent layer 20 in the mountarea A_(M) of the gap G is about 0.77 g/cc and the compressed density ofthe combined non-intumescent layer 13 and a strip 92 or 94 in each sealarea A_(S) of the gap G is equal to about 0.40 g/cc. For a gap equal toabout 8 mm, it is believed that the non-intumescent layer 13 may have aminimum basis weight of about 2000 g/m², the intumescent layer 20 mayhave a minimum basis weight of about 4695 g/m², and each non-intumescentstrip 92 and 94 may have a minimum basis weight of about 1200 g/m² andwherein the compressed density of the combined non-intumescent layer 13and intumescent layer 20 in the mount area A_(M) of the gap G is about0.77 g/cc and the compressed density of the combined non-intumescentlayer 13 and a strip 92 or 94 in each seal area A_(S) of the gap G isequal to about 0.40 g/cc. In each of the prophetic examples set outabove, in the mount area A_(M) of the gap G where the intumescent andnon-intumescent layers 20 and 13 are positioned, it is believed that theintumescent layer 20 will fill approximately 60% of the gap G, and thenon-intumescent layer 13 will fill about 40% of the gap G. In each ofthe prophetic examples set out above, in the seal areas A_(S) of the gapG where the non-intumescent layer 13 and a non-intumescent strip 92 or94 are positioned, it is believed that the non-intumescent layer 13 willfill approximately 60% of the gap, and the non-intumescent strip 92 or94 will fill approximately 40% of the gap G.

In the FIG. 7 embodiment, the intumescent layer 20 is shown positionedadjacent to the catalytic converter metal housing 50. However, for someapplications, such as low temperature applications, the intumescentlayer 20 may be positioned adjacent to the catalyst support element 40.In such an embodiment, the non-intumescent strips 92, 94 may also bepositioned adjacent to the catalyst support element 40.

A multilayer mat 100 constructed in accordance with a seventh embodimentis illustrated in FIG. 8, where like reference numerals indicate likeelements. The mat 100 comprises an inner non-intumescent layer 13comprising ceramic fibers and has a width W₁ defined by opposite lateraledges 14 and 16 and a length L₁. The mat 100 further comprises anintumescent layer 72 comprising intumescent material and has a width W₃defined by opposite lateral edges 74 and 76 and a length substantiallyequal to length L₁ of the non-intumescent layer 13. In the illustratedembodiment, the width W₃ of the intumescent layer 72 is less than thewidth W₁ of the non-intumescent layer 13. Further, the intumescent layer72 is positioned relative to the non-intumescent layer 13 such thatlateral edge 74 is positioned within the two lateral edges 14 and 16 ofthe non-intumescent layer 13 and lateral edge 76 is substantiallyin-line with lateral edge 16.

The multilayer mat 100 further comprises a strip 102 of non-intumescentmaterial. The non-intumescent strip 102 is positioned over a first outerportion 18A of the non-intumescent layer 13. The non-intumescent strip102 has a width W₄ and a length substantially equal to length L₁ of theinner non-intumescent layer 13. In the illustrated embodiment, thesummation of the width W₃ of the intumescent layer 72 and the width W₄of the non-intumescent strip 102 is substantially equal to the width W₁of the inner non-intumescent layer 13.

In FIG. 9, the mat 100 is shown provided within a metal housing 50 so asto support and maintain a catalyst support element 40 within the housing50. The mat 100, housing 50 and support element 40 define a catalyticconverter 480.

The non-intumescent strip 102 can be formed from a substantiallyresilient non-intumescent material for use in the catalytic converter480 such that once the mat 100 and the catalyst support element 40 arepositioned within the metal housing 50, the strip 162 sufficientlyexpands in a seal area A_(S) of a gap G, between an inner wall of thehousing 50 and the support element 40, see FIG. 9, so as to seal thelateral edge 74 of the intumescent layer 72, as the gap G expands withincreasing temperatures. In other words, at least the strip 102 isresilient enough to exert a sufficient pressure to seal the gap G andprotect the lateral edge 74 of the intumescent layer 72, whether the gapG is at its smallest (i.e., at ambient temperature) or biggest (i.e., atthe highest operating temperature). It is desirable for at least thestrip 102 to also be durable enough to survive cycling of the gap Gbetween its smallest and biggest over the desired life of the pollutioncontrol device. It can be preferable for the non-intumescent layer 13 toalso exhibit this degree of resilience and durability. Hence, theintumescent layer lateral edge 74 is substantially sealed from directexposure to high temperature exhaust gases flowing through the catalyticconverter 480. It is noted that the inner non-intumescent layer 13 maybe formed from a material which is less resilient than thenon-intumescent strip 102. For example, the non-intumescent strip 102may be formed from one of the same materials, set out above, from whichthe layer 12 in the FIG. 1 embodiment is formed. The intumescent layer72 may be formed from one of the same intumescent materials, set outabove, from which the intumescent layer 20 in the FIG. 1 embodiment isformed. The non-intumescent layer 13 may be formed from the samenon-intumescent material, set out above, from which the non-intumescentlayer 13 in the FIG. 4A embodiment is formed.

It is noted that in the FIG. 9 embodiment, the lateral edge 76 of theintumescent layer 72 is not sealed by the non-intumescent layer 13.However, because the lateral edge 76 is not positioned in the incomingpath of the exhaust gases, loss of intumescent material from lateraledge 76 may be minimal for some catalytic converter designs.

In the FIG. 9 embodiment, the intumescent layer 72 is shown positionedadjacent to the catalytic converter metal housing 50. However, for someapplications, such as low temperature applications, the intumescentlayer 72 may be positioned adjacent to the catalyst support element 40.In such an embodiment, the non-intumescent strip 102 may also bepositioned adjacent to the catalyst support element 40.

A multilayer mat 110 constructed in accordance with an eighth embodimentis illustrated in FIG. 10, where like reference numerals indicate likeelements. The mat 110 is similar to mat 100 illustrated in FIGS. 8 and9, except that the width W₆ of an intumescent layer 112 is less than thewidth W₃ of the intumescent layer 72 in the FIG. 8 embodiment. Theintumescent layer 112 has lateral edges 114 and 116. As illustrated inFIG. 10, the intumescent layer 112 defines an outermost layer and ispositioned adjacent to the non-intumescent layer 13.

The mat 110 is used to support and mount a support element 40 in a metalhousing 550 so as to define a catalytic converter 580, see FIG. 10. Themetal housing 550 is formed so as to include a recess 550A, which, inthe illustrated embodiment, extends circumferentially about the entiretyof the housing 550. The housing recess 550A is shaped in X and Zdirections so as to receive the intumescent layer 112 and substantiallyshield the intumescent layer lateral edge 116 from exhaust gases passingthrough the catalytic converter 580 in a left to right direction asviewed in FIG. 10. Hence, the intumescent layer lateral edge 116 issubstantially sealed from exposure to high temperature exhaust gasesflowing through the catalytic converter 580.

As in the FIG. 8 embodiment, the non-intumescent strip 102 is formedfrom a substantially resilient non-intumescent material for use in thecatalytic converter 580 such that once the mat 110, and the catalystsupport element 40 are positioned within the metal housing 550, thestrip 102 sufficiently expands in a gap between the support element 40and an inner wall of the housing 550 so as to seal the lateral edge 114of the intumescent layer 112, as the gap expands with increasingtemperatures. In other words, at least the strip 102 is resilient enoughto exert a sufficient pressure to seal the gap G and protect the lateraledge 114 of the intumescent layer 112, whether the gap G is at itssmallest (i.e., at ambient temperature) or biggest (i.e., at the highestoperating temperature). It is desirable for at least the strip 102 toalso be durable enough to survive cycling of the gap G between itssmallest and biggest over the desired life of the pollution controldevice. It can be preferable for the non-intumescent layer 13 to alsoexhibit this degree of resilience and durability. Hence, the intumescentlayer lateral edge 114 is substantially sealed from direct exposure toincoming high temperature exhaust gases flowing through the catalyticconverter 580. The intumescent layer 112 may be formed from one of thesame intumescent materials, set out above, from which the intumescentlayer 20 in the FIG. 1 embodiment is formed. The non-intumescent layer13 may be formed from the same non-intumescent material, set out above,from which the non-intumescent layer 13 in the FIG. 4A embodiment isformed. The non-intumescent strip 102 may be formed from one of the samematerials, set out above, from which the layer 12 in the FIG. 1embodiment is formed.

A multilayer mat 120 constructed in accordance with an ninth embodimentis illustrated in FIG. 11, where like reference numerals indicate likeelements. The mat 120 comprises an inner non-intumescent layer 13comprising ceramic fibers and has a width W₁ defined by opposite lateraledges 14 and 16 and a length L₁. The mat 120 further comprises anintumescent layer 112 comprising intumescent material and having a widthW₆ defined by opposite lateral edges 114 and 116 and a lengthsubstantially equal to length L₁ of the non-intumescent layer 13. In theillustrated embodiment, the width W₆ of the intumescent layer 112 isless than the width W₁ of the non-intumescent layer 13. Further, theintumescent layer 112 is positioned relative to the non-intumescentlayer 13 such that the lateral edges 114 and 116 are positioned withinthe two lateral edges 14 and 16 of the non-intumescent layer 13.

The multilayer mat 120 further comprises a strip 122 of non-intumescentmaterial. The non-intumescent strip 122 is positioned over an outerportion 18B of the non-intumescent layer 13. The non-intumescent strip122 has a width W₅ and a length substantially equal to the lengths ofthe inner non-intumescent layer 13 and the intumescent layer 112.

In FIG. 12, the mat 120 is shown provided within a metal housing 650 soas to support and maintain a catalyst support element 40 within thehousing 650. The mat 120, housing 650 and support element 40 define acatalytic converter 680.

Preferably, the non-intumescent strip 122 is formed from a substantiallyresilient non-intumescent material for use in the catalytic converter680 such that once the mat 120 and the catalyst support element 40 arepositioned within the metal housing 650, the strip 122 sufficientlyexpands in a gap between the support element 40 and an inner wall of thehousing 650 so as to seal the lateral edge 116 of the intumescent layer112, as the gap expands with increasing temperatures. In other words, atleast the strip 122 is resilient enough to exert a sufficient pressureto seal the gap G and protect the lateral edge 116 of the intumescentlayer 112, whether the gap G is at its smallest (i.e., at ambienttemperature) or biggest (i.e., at the highest operating temperature). Itis desirable for at least the strip 122 to also be durable enough tosurvive cycling of the gap G between its smallest and biggest over thedesired life of the pollution control device. It can be preferable forthe non-intumescent layer 13 to also exhibit this degree of resilienceand durability. Hence, the intumescent layer lateral edge 116 issubstantially sealed from exposure to high temperature exhaust gasesflowing through the catalytic converter 680.

The metal housing 650 is formed so as to include a recess 650A, which,in the illustrated embodiment, extends about the entirety of the housing650, see FIG. 12. The housing recess 650A is shaped in X and Zdirections so as to receive the intumescent layer 112 and substantiallyshield the intumescent layer lateral edge 114 from exhaust gases passingthrough the catalytic converter 680. Hence, the intumescent layerlateral edge 114 is substantially sealed from direct exposure toincoming high temperature exhaust gases flowing through the catalyticconverter 680. The intumescent layer 112 may be formed from one of thesame intumescent materials, set out above, from which the intumescentlayer 20 in the FIG. 1 embodiment is formed. The non-intumescent layer13 may be formed from the same non-intumescent material, set out above,from which the non-intumescent layer 13 in the FIG. 4A embodiment isformed. The non-intumescent strip 122 may be formed from one of the samematerials, set out above, from which the layer 12 in the FIG. 1embodiment is formed.

It is noted that the multilayer mats, set out above, may alternativelybe used to secure a pollution control element such as a filter elementwithin a housing of an exhaust filter or trap. It is further noted thatsuch pollution control devices, according to the present invention, canbe used in the exhaust system of an internal combustion engine (e.g., avehicle exhaust system, a power generator exhaust system).

The multilayer mats are typically flexible. The mats usually can behandled and wrapped around a pollution control element in a pollutioncontrol device without breaking or cracking. When wrapped around apollution control element, the ends of the multilayer mat can meet in avariety of junctions as discussed in pending U.S. patent applicationSer. No. 10/824,029, entitled “SANDWICH HYBRID MOUNTING MAT,” and filedon Apr. 14, 2004, the disclosure of which is incorporated herein byreference.

As noted above, the non-intumescent layer 12 and non-intumescent strips102 and 122 may be more resilient than the non-intumescent layer 13.Further, the non-intumescent strips 92 and 94 may be more resilient thanthe non-intumescent layer 13 or vice versa. Hence, the non-intumescentlayer 13 may be formed from a material having a different compositionfrom a material used to form the non-intumescent layer 12 andnon-intumescent strips 92, 94, 102, 122.

Presuming that the catalytic converters 60, 180, 380, 80, 280, 480, 580and 680 are intended for use in high temperature applications, forexample, at temperatures greater than about 900 degrees C., theintumescent layer 20 in the embodiments of FIGS. 1-4, 4A, 6-7, theintumescent layer 72 in the embodiments of FIGS. 5, 5A, 8-9, and theintumescent layer 112 of the embodiment of FIGS. 10 and 11-12, may bereplaced by a comparably narrow non-intumescent layer that has at leastone lateral edge needing protection from exposure to mechanical erosionforces generated by the impact of and/or high temperatures associatedwith exhaust gases passing through the corresponding catalytic converter60, 180, 380, 80, 280, 480, 580 and 680 that contact the at least onelateral edge of the non-intumescent layer. Some non-intumescentmaterials may be damaged if exposed to high temperature exhaust gases,which damage can result in increased erosion of the non-intumescentmaterial if directly exposed to such exhaust gases. Non-intumescentmaterial lost due to erosion can reduce the mounting force of thecorresponding mat as well as result in eroded material passing into andblocking passageways in the pollution control element (e.g., a catalystsupport element 40 or a exhaust filter element). In propheticembodiments set out here, a narrower non-intumescent layer can beprotected by a wider non-intumescent layer, with at least one lateraledge of the wider non-intumescent layer being sufficiently resilient anddurable to withstand exposure to mechanical erosion forces generated bythe impact of and high temperatures associated with exhaust gases,passing through the pollution control device, that contact the at leastone lateral edge of the narrower non-intumescent layer. The narrownon-intumescent layer may also be one having at least one lateral edgethat needs protection from exposure to the maximum operating temperatureof the pollution control device, as well as to the exhaust gas erosionforces.

A prophetic example of a non-intumescent layer that may need protectionfrom high temperatures associated with exhaust gases passing through thepollution control device and/or radiated by the catalyst support elementcomprises a layer formed from a high silica glass fiber mat commerciallyavailable from REFRASIL® under the product designation “RB 1800.” Aprophetic example of a non-intumescent layer that may need protectionfrom mechanical forces generated by the exhaust gases passing through acatalytic converter comprises a layer formed from a refractory ceramicfiber mat commercially available from the 3M Company (St. Paul, Minn.)under the trade designation “INTERAM 900HT.” Prophetic examples of anon-intumescent layer that may need protection from high temperaturesassociated with exhaust gases passing through the pollution controldevice and/or radiated by the catalyst support element and mechanicalforces generated by the exhaust gases passing through a catalyticconverter comprises a layer formed from refractory ceramic fiberscommercially available from Unifrax under the product designation“FIBERFRAX 6000 and 7000 Series” or refractory ceramic fiberscommercially available from Thermal Ceramics under the productdesignation “KAOWOOL.”

Presuming that the catalytic converters 60, 180, 380, 80, 280, 480, 580and 680 are intended for use in low temperature applications, forexample, at temperatures below about 900 degrees C., the intumescentlayer 20 in the embodiments of FIGS. 1-4, 4A, 6-7, the intumescent layer72 in the embodiments of FIGS. 5, 5A, 8-9, and the intumescent layer 112of the embodiment of FIGS. 10 and 11-12, may be replaced by anon-intumescent layer that needs protection from mechanical forcesgenerated by the exhaust gases passing through the correspondingcatalytic converter 60, 180, 380, 80, 280, 480, 580 and 680. Propheticexamples of non-intumescent layers that may need protection frommechanical forces generated by the exhaust gases passing through acatalytic converter include those set out above which comprise a layerformed from a refractory ceramic fiber mat commercially available fromthe 3M Company (St. Paul, Minn.) under the trade designation “INTERAM900HT” or a layer formed from refractory ceramic fibers commerciallyavailable from Unifrax under the product designation “FIBERFRAX 6000 and7000 Series” or refractory ceramic fibers commercially available fromThermal Ceramics under the product designation “KAOWOOL.” Hence, in theprophetic embodiments set out in this paragraph, a narrowernon-intumescent layer may be protected from mechanical forces by a widernon-intumescent layer.

Presuming that the catalytic converters 60, 180, 380, 80, 280, 480, 580and 680 are intended for use in low temperature applications, forexample, at temperatures below about 900 degrees C., the non-intumscentlayer 12 in the embodiments of FIGS. 1-4 and 5, and the non-intumescentstrips 92, 94 in the embodiment of FIG. 6-7, the non-intumescent strip102 in the embodiments of FIGS. 8-9 and 10 and the non-intumescent strip122 in the embodiment of FIGS. 11-12, may be replaced by an intumescentlayer or strip(s) that is capable of withstanding mechanical forcesgenerated by exhaust gases passing through a catalytic converter. Oncethe mat and the catalyst support element 40 have been mounted within themetal housing 50, and the wider intumescent layer or the strip(s) isheated, outer portions of the wider intumescent layer or the strip(s) incombination with the non-intumescent layer 13 will fill the gap G, in atleast the seal areas A_(S), between an inner wall of the housing 50 andthe support element 40, so as to seal the gap G and protect the lateraledges of the narrower intumescent or non-intumescent layer. Hence, inthe prophetic embodiments set out in this paragraph, a narrowernon-intumescent or intumescent layer may be protected from mechanicalforces by a wider intumescent layer or one or more intumescent strips incombination with a wider non-intumescent layer 13.

Prophetic examples of intumescent layers/strips that do not needprotection from mechanical forces generated by exhaust gases passingthrough a catalytic converter include those formed from one of therefractory ceramic fiber mats commercially available from the 3M Company(St. Paul, Minn.) under the trade designations “T-100HD,” T-200HD,” and“T-550,” and a refractory ceramic fiber mat commercially available fromUnifrax under the product designation “AV2.”

It is also contemplated that the non-intumescent layer 13 in theembodiments of FIGS. 4A, 5A, 6-7, 8-9, 10 and 11-12 may be replaced byan intumescent layer for low temperature applications.

The intumescent layer 720 in the embodiment of FIG. 13 may be replacedby a non-intumescent layer that needs protection from mechanical forcesgenerated by the exhaust gases passing through the catalytic converter760. Hence, outer portions 718A and 718B of the wider non-intumescentlayer 712 sufficiently expand in the seal areas A_(S) of a gap G,between an inner wall of the housing 50 and the support element 40, soas to seal the lateral edges of the narrower non-intumescent layer thatneeds protection from mechanical forces generated by exhaust gasespassing through the catalytic converter 760, as the gap G expands withincreasing temperatures. A non-intumescent layer that needs protectionfrom mechanical forces generated by the exhaust gases passing through acatalytic converter may be made from a refractory ceramic fiber matcommercially available from the 3M Company (St. Paul, Minn.) under thetrade designation “INTERAM 900HT.” Presuming the mat 710 will be used inlow temperature applications, the non-intumescent layer that needsprotection from mechanical forces generated by the exhaust gases passingthrough a catalytic converter may be made from refractory ceramic fiberscommercially available from Unifrax under the product designation“FIBERFRAX 6000 and 7000 Series” or refractory ceramic fiberscommercially available from Thermal Ceramics under the productdesignation “KAOWOOL.”

Each non-intumescent layer or strip contains inorganic fibers. Anyinorganic fiber that is known to be suitable for use in a mounting matfor a pollution control device can be selected. For example, theinorganic fibers can be alumina fibers, mullite fibers, quartz fibers,silicon carbide fibers, silicon nitride fibers, metal fibers,aluminosilicate fibers, magnesium aluminosilicate fibers,aluminoborosilicate fibers, zirconia fibers, titania fibers, and thelike. The fibers can be amorphous, crystalline, or a combinationthereof.

Quartz fibers are commercially available under the trade designation“ASTROQUARTZ” from J.P. Stevens, Inc. (Slater, N.C.). Silicon carbidefibers are commercially available from Nippon Carbon (Tokyo, Japan)under the trade designation “NICALON” or from Textron SpecialtyMaterials (Lowell, Mass.) under the trade designation “TYRANNO”. Siliconnitride fibers are commercially available from Toren EnergyInternational Corp. (New York, N.Y.). Metal fibers are commerciallyavailable from Beckaert (Zweregan, Belgium) under the trade designation“BEKI-SHELD GR 90/C2/4” and from Ribbon Technology Corp. (Gahana, Ohio)under the trade designation “RIBTEC”.

In some embodiments of the non-intumescent layer(s) or strip(s), theinorganic fibers are glass fibers. As used herein, the term “glassfibers” refers to inorganic fibers that are prepared from an inorganicfusion material that has been cooled without substantialcrystallization. The glass fibers are amorphous as determined usingeither x-ray diffraction or transmission electron microscopictechniques. The glass fibers, at least in some applications, are shotfree (i.e., the fibers contain no greater than 5 weight percent shot, nogreater than 3 weight percent shot, no greater than 2 weight percentshot, no greater than 1 weight percent shot, or no greater than 0.5weight percent shot). As used herein, the term “shot” refers tonon-fibrous particles that can be a by-product of some inorganic fiberformation processes.

Suitable glass fibers are often magnesium aluminosilicate fibers. Suchglass fibers can contain at least 50 weight percent SiO₂, at least 8weight percent Al₂O₃, and at least 1 weight percent magnesium oxide. Forexample, magnesium aluminosilicate fibers can contain 50 to 70 weightpercent, 50 to 60 weight percent, 60 to 70 weight percent, or 55 to 65weight percent SiO₂; 8 to 30 weight percent, 10 to 20 weight percent, or20 to 30 weight percent Al₂O₃; and 1 to 15 weight percent, 1 to 12weight percent, 1 to 10 weight percent, or 1 to 8 weight percentmagnesium oxide. Additional oxides can be present such as sodium oxide,potassium oxide, boron oxide, calcium oxide, and the like.

Specific examples of magnesium aluminosilicate glass fibers are E-glassfibers, S-glass fibers, S2-glass fibers, and R-glass fibers. E-glassfibers often contain about 55 weight percent SiO₂, about 11 weightpercent Al₂O₃, about 6 weight percent B₂O₃, about 18 weight percent CaO,about 5 weight percent MgO, and about 5 weight percent other oxides.S-glass and S2-glass fibers typically contain about 65 weight percentSiO₂, about 25 weight percent Al₂O₃, and about 10 weight percent MgO.R-glass fibers usually contain about 60 weight percent SiO₂, about 25weight percent Al₂O₃, about 9 weight percent CaO, and about 6 weightpercent MgO. E-glass fibers, S-glass fibers, and S2-glass fibers arecommercially available from Advanced Glassfiber Yarns, LLC (Aiken, S.C.)and Owens-Corning Fiberglass Corp. (Granville, Ohio). R-glass fibers arecommercially available from Saint-Gobain Vetrotex (Herzogenrath,Germany).

Various refractory ceramic fibers can be used in the non-intumescentlayer(s) or strip(s). In some embodiments, the ceramic fibers areamorphous and contain mainly Al₂O₃ and SiO₂. Small amounts of otheroxides can be present. The weight ratio of Al₂O₃ to SiO₂ (Al₂O₃: SiO₂)is usually greater than or equal to 20:80, 30:70, 35:65, 40:60. 45:55,50:50, 55:45, 60:40, or 70:30. The ceramic fibers typically include atleast 30 weight percent SiO₂ and at least 20 weight percent Al₂O₃. Forexample, suitable ceramic fibers can contain SiO₂ in an amount of 30 to80 weight percent and Al₂O₃ in an amount of 20 to 70 weight percentweight percent based on the weight of the fibers. In some specificexamples, the ceramic fibers can contain SiO₂ in an amount of 40 to 60weight percent and alumna in an amount of 40 to 60 weight percent basedon the weight of the fibers. In other specific examples, the ceramicfibers can contain SiO₂ in an amount of 45 to 55 weight percent andAl₂O₃ in an amount of 45 to 55 weight percent based on the weight of thefibers.

Exemplary amorphous ceramic fibers that contain mainly Al₂O₃ and SiO₂include, but are not limited to, those commercially available fromThermal Ceramics (Augusta, Ga.) under the trade designation “KAOWOOL HABULK” with 50 weight percent SiO₂ and 50 weight percent Al₂O₃ based onthe weight of the fibers; from Thermal Ceramics under the tradedesignation “CERAFIBER” with 54 weight percent SiO₂ and 46 weightpercent Al₂O₃ based on the weight of the fiber; from Thermal Ceramicsunder the trade designation “KAOWOOL D73F” with 54 weight percent SiO₂and 46 weight percent Al₂O₃ based on the weight of the fiber; from Rath(Wilmington, Del.) under the trade designation “RATH 2300 RT” with 52weight percent SiO₂, 47 weight percent Al₂O₃, and no greater than 1weight percent Fe₂O₃, TiO₂, and other oxides based on the weight of thefibers; from Rath under the trade designation “RATH ALUMINO-SILICATECHOPPED FIBER” with 54 weight percent SiO₂, 46 weight percent Al₂O₃, andno greater than 1 weight percent of other oxides based on the weight ofthe fiber; from Vesuvius (Buffalo, N.Y.) under the trade designation“CER-WOOL RT” with 49 to 53 weight percent SiO₂, 43 to 47 weight percentAl₂O₃, 0.7 to 1.2 weight percent Fe₂O₃, 1.5 to 1.9 weight percent TiO₂,and no greater than 1 weight percent other oxides based on the weight ofthe fibers; from Vesuvius under the trade designation “CER-WOOL LT” with49 to 57 weight percent SiO₂, 38 to 47 weight percent Al₂O₃, 0.7 to 1.5weight percent Fe₂O₃, 1.6 to 1.9 weight percent TiO₂, and 0 to 0.5weight percent other oxides based on the weight of the fibers; and fromVesuvius under the trade designation “CER-WOOL HP” with 50 to 54 weightpercent SiO₂, 44 to 49 weight percent Al₂O₃, 0 to 0.2 weight percentFe₂O₃, 0 to 0.1 weight percent TiO₂, and no greater than 0.5 weightpercent other oxides based on the weight of the fibers.

In other embodiments, the ceramic fibers are amorphous and containmainly SiO₂, Al₂O₃, and ZrO₂. Small amounts of other oxides can bepresent. The weight ratio of Al₂O₃ to SiO₂ (Al₂O₃: SiO₂) is greater thanor equal to 20:80, 30:70, 35:65, 40:60. 45:55, 50:50, 55:45, 60:40, or70:30. The fibers contain at least 3 weight percent ZrO₂, at least 30weight percent SiO₂, and at least 20 weight percent Al₂O₃ based on theweight of the fiber. In some embodiments, the fibers contain ZrO₂ in anamount up to 5 weight percent, up to 7 weight percent, up to 10 weightpercent, up to 12 weight percent, up to 15 weight percent, up to 16weight percent, up to 20, or up to 25 weight percent based on the weightof the fibers. The ceramic fibers can contain SiO₂ in an amount of 30 to70, 40 to 65, 45 to 60, 45 to 55, or 50 to 60 weight percent based onthe weight of the fibers. The ceramic fibers can contain Al₂O₃ in anamount of 20 to 60, 25 to 50, 25 to 45, 25 to 40, 25 to 35, to 50, or 30to 40 weight percent based on the weight of the fibers. In some specificexamples, the ceramic fibers contain 25 to 50 weight percent Al₂O₃, 40to 60 weight percent SiO₂, and 3 to 20 weight percent ZrO₂ based on theweight of the fibers. In other specific examples, the ceramic fiberscontain 30 to 40 weight percent Al₂O₃, 45 to 60 weight percent SiO₂, and5 to 20 weight percent ZrO₂ based on the weight of the fibers.

Exemplary amorphous ceramic fibers that contain SiO₂, Al₂O₃, and ZrO₂are commercially available from Thermal Ceramics (Augusta, Ga.) underthe trade designation “KAOWOOL ZR” and “CERACHEM” with 50 weight percentSiO₂, 35 weight percent Al₂O₃, and 15 weight percent ZrO₂ based on theweight of the fiber; from Unifrax (Tonawonda, N.Y.) under the tradedesignation “UNIFRAX FIBERFRAX FIBERMAT” with 52 to 57 weight percentSiO₂, 29 to 47 weight percent Al₂O₃, and no greater than 18 weightpercent ZrO₂ based on the weight of the fibers; from Unifrax under thetrade designation “UNIFRAX FIBERFRAX DURABACK” with 50 to 54 weightpercent SiO₂, 31 to 35 weight percent Al₂O₃, 5 weight percent ZrO₂, 1.3weight percent Fe₂O₃, 1.7 weight percent TiO₂, 0.5 weight percent MgO,and no greater than 7 weight percent CaO based on the weight of thefibers; from Rath (Wilmington, Del.) under the trade designation “RATH2600 HTZ” with 48 weight percent SiO₂, 37 weight percent Al₂O₃, 15weight percent ZrO₂, and no greater than 1 weight percent other oxidesbased on the weight of the fibers; and from Vesuvius (Buffalo, N.Y.)under the trade designation “CER-WOOL HTZ” with 44 to 51 weight percentSiO₂, 33 to 37 weight percent Al₂O₃, 13 to 19 weight percent ZrO₂, 0.1to 0.6 weight percent Fe₂O₃, 0.1 to 0.6 weight percent TiO₂, and nogreater than 1 weight percent other oxides based on the weight of thefibers.

In some embodiments of the non-intumescent layer(s) or strip(s), theceramic fibers have a bulk shrinkage no greater than 10 percent, nogreater than 8 percent, no greater than 6 percent, no greater than 4percent, no greater than 3 percent, no greater than 2 percent, or nogreater than 1 percent using the Thermal Mechanical Analyzer (TMA) test.The ceramic fibers typically shrink at least 0.5 percent. In someembodiments, the ceramic fibers have a bulk shrinkage of 0.5 to 2percent, 0.5 to 3 percent, 0.5 to 5 percent, or 0.5 to 6 percent.

In the TMA test, a sample under a load (e.g., 50 psi or 345 N/m²) isheated to 1000° C. and then cooled. The caliper of the sample can bemeasured during both the heating and cooling cycles at 750° C. tocalculate percent shrinkage. The percent shrinkage is equal to thedifference in the caliper at 750° C. during the heating and cooling stepmultiplied by 100 and divided by the caliper at 750° C. during theheating step. The TMA test can be used to characterize the ceramicfibers or an non-intumescent layer prepared from ceramic fibers. Most orall of the organic materials that may be present in a non-intumescentlayer are removed by time the temperature of the Thermal MechanicalAnalyzer reaches 750° C.

Examples of ceramic fibers having a bulk shrinkage no greater than 10percent as supplied (i.e., the fibers can be used as supplied without aheat-treatment) include, but are not limited to, fibers that arecrystalline and that contain both Al₂O₃ and SiO₂. The weight ratio ofAl₂O₃ to SiO₂ (Al₂O₃: SiO₂) can be greater than or equal to 60:40,65:35, 70:30, 72:28, 75:25, 80:20, 90:10, 95:5, 96:4, 97:3, or 98:2. Insome specific examples, the ceramic fibers contain 60 to 98 weightpercent Al₂O₃ and 2 to 40 weight percent SiO₂ based on the weight of thefibers. In other specific examples, the ceramic fibers contain 70 to 98weight percent Al₂O₃ and 2 to 30 weight percent SiO₂ based on the weightof the fibers. Traces of other oxides can be present. As used herein,the term “trace” refers to an amount no greater than 2 weight percent,no greater than 1 weight percent, or no greater than 0.5 weight percent.

Suitable ceramic fibers that are crystalline and have a bulk shrinkageno greater than 10 percent include, but are not limited, to thosecommercially available from Mitsubishi Chemical (Tokyo, Japan) under thetrade designation “MAFTEC” (e.g., MLS1, MLS2, and MLS3) with 28 weightpercent SiO₂ and 72 weight percent Al₂O₃ based on the weight of thefibers; from Saffil Limited (Widness Cheshire, U.K.) under the tradedesignation “SAFFIL” (e.g., SF, LA Bulk, HA Bulk, HX Bulk) with 3 to 5weight percent SiO₂ and 95 to about 97 weight percent Al₂O₃ based on theweight of the fibers; and from Unifrax (Tonawonda, N.Y.) under the tradedesignation “UNIFRAX FIBERFRAX FIBERMAX” with 27 weight percent SiO₂ and72 weight percent Al₂O₃ based on the weight of the fibers.

Further examples of ceramic fibers that are crystalline and have a bulkshrinkage no greater than 10 percent as supplied are aluminoborosilicatefibers. These fibers typically contain Al₂O₃ in an amount of at least 50weight percent, SiO₂ in an amount no greater than 50 weight percent, andB₂O₃ in an amount no greater than 25 weight percent based on the weightof the fibers. Some specific aluminoborosilicate fibers contain 50 to 75weight percent Al₂O₃, 25 to 50 weight percent SiO₂, and 1 to 25 weightpercent B₂O₃ based on the weight of the fibers. Such aluminoborosilicatefibers are commercially available under the trade designation “NEXTEL312” and “NEXTEL 440” from 3M Company (St. Paul, Minn.).

At least some of these ceramic fibers that are crystalline and that havea bulk shrinkage no greater than 10 percent as supplied by themanufacturer are prepared using a sol-gel process. In a sol-gel process,the ceramic fibers are formed by spinning or extruding a solution,dispersion, or viscous concentrate. The sol-gel process, which isfurther described in U.S. Pat. No. 3,760,049 (Borer et al.), can includeextrusion of the solution, dispersion, or concentrate through orificesto form green fibers that are then fired to form ceramic fibers. Thesolution, dispersion, or concentrate contains the oxides or theprecursors to the oxides that are in the fibers.

In some embodiments, commercially available amorphous ceramic fibers canbe heat-treated to provide ceramic fibers that have a bulk shrinkage nogreater than 10 percent. The ceramic fibers that can be heat-treated toprovide fibers having a bulk shrinkage no greater than 10 percenttypically are melt-blown or melt-spun from a mixture of Al₂O₃ and SiO₂or a mixture of Al₂O₃ and SiO₂ with other oxides such as B₂O₃, P₂O₅, orZrO₂. Exemplary amorphous ceramic fibers that can be heat-treatedinclude, but are not limited to, ceramic fibers commercially availablefrom Thermal Ceramics (Augusta, Ga.) under the trade designation“KAOWOOL HA BULK”, “CERAFIBER”, “KAOWOOL D73F”, “KAOWOOL ZR”, or“CERACHEM”; from Rath (Wilmington, Del.) under the trade designation“RATH 2300 RT”, “RATH ALUMINO-SILICIATE CHOPPED FIBER”, or “RATH 2600HTZ”; from Vesuvius (Buffalo, N.Y.) under the trade designation“CER-WOOL RT”, “CER-WOOL LT”, or “CER-WOOL HTZ”, or “CER-WOOL HP”; andfrom Unifrax (Tonawonda, N.Y.) under the trade designation “UNIFRAXFIBERFRAX FIBERMAT” or “UNIFRAX FIBERFRAX DURABACK”.

The ceramic fibers tend to devitrify (i.e., change, at least in part,from an amorphous state into a microcrystalline or crystalline state)during the heat-treatment process. Usually, only a portion of theindividual ceramic fiber undergoes devitrification. That is, afterheat-treatment, the individual ceramic fibers contain amorphous materialas well as crystalline material, microcrystalline material, or acombination of crystalline and microcrystalline material.

Techniques such as transmission electron microscopy and x-raydiffraction can be used to characterize the amorphous, crystalline, ormicrocrystalline nature of inorganic fibers. As used herein, the term“amorphous” refers to inorganic fibers that are free of crystalline ormicrocrystalline regions. If the inorganic fibers are amorphous, nodiffraction peaks (i.e., no diffraction pattern) can be detected usingeither transmission electron microscopy or x-ray diffraction. If theinorganic fiber contains regions having a small crystalline size (i.e.,microcrystalline), diffraction peaks (i.e., a diffraction pattern) canbe detected using transmission electron microscopy but not using x-raydiffraction. As used herein, the term “microcrystalline” refers toinorganic fibers that have at least some regions with a crystallinecharacter and that have a crystal size detectable with transmissionelectron microscopy but not with x-ray diffraction. If the inorganicfibers contain regions having a larger crystalline size (i.e.,crystalline), a diffraction pattern can be obtained using x-raydiffraction. As used herein, the term “crystalline” refers to inorganicfibers that have at least some regions with a crystalline character andthat have a crystal size detectable with x-ray diffraction. The smallestcrystal sizes detectable using x-ray diffraction typically results in abroad diffraction pattern without well-defined peaks. Narrower peaksindicate a larger crystalline size. The width of the diffraction peakscan be used to determine the crystalline size. The inorganic fibers thatare crystalline are usually polycrystalline rather than being singlecrystals.

In some applications, the ceramic fibers are heat-treated at atemperature of at least 700° C. For example, the ceramic fibers can beheat-treated at a temperature of at least 800° C., at a temperature ofat least 900° C., at a temperature of at least 1000° C., or at atemperature of at least 1100° C. Suitable heat-treatment temperaturescan vary depending on the composition of the ceramic fibers and the timethe ceramic fibers are held at the heat-treatment temperature. Suitableheat-treatment methods and suitable heat-treated ceramic fibers arefurther described, for example, in International Patent Application WO99/46028 (Fernando et al.) and U.S. Pat. No. 5,250,269 (Langer), thedisclosure of which are incorporated herein by reference.

There is a time-temperature relationship associated with the size ofcrystals or microcrystals that form during the heat-treatment process.For example, the ceramic fibers can be heat-treated at lowertemperatures for longer periods of time or at higher temperatures forshorter periods of time to produce a comparable state of crystallinityor microcrystallinity. The time at the heat-treatment temperature can beup to 1 hour, up to 40 minutes, up to 30 minutes, up to 20 minutes, upto 10 minutes, up to 5 minute, up to 3 minutes, or up to 2 minutes. Forexample, the heat-treatment temperature can be chosen to use arelatively short heat-treatment time such as up to 10 minutes.

The temperature of the heat-treatment can be chosen to be at least 20°C., at least 30° C., at least 40° C., at least 50° C., at lest 60° C.,at least 70° C., at least 80° C., at least 90° C., or at least 100° C.above the devitrification temperature (i.e., the temperature at whichthe ceramic fibers change from being an amorphous material to being amicrocrystalline or crystalline material). Suitable heat-treatment timesand temperatures for the ceramic fibers can be determined usingtechniques such as, for example, Differential Thermal Analysis (DTA).The temperature for Al₂O₃—SiO₂ fibers is typically in the range of 700°C. to 1200° C., in the range of 800° C. to 1200° C., in the range of900° C. to 1200° C., or in the range of 950° C. to 1200° C.

A ceramic fiber that is completely amorphous usually shrinks more thanceramic fiber that contain regions that are microcrystalline,crystalline, or a combination thereof. Ceramic fibers that are at leastpartially crystalline or microcrystalline can be fabricated intomounting mats that can be repeatedly heated to a temperature suitablefor use in a pollution control device and then cooled. Microcrystallineor crystalline ceramic fibers tend to be resistant to further shrinkagethat could negatively impact the performance of the non-intumescentlayer.

For ceramic fibers that are subjected to heat-treatment, the brittlenessof the fibers can be balanced with the low bulk shrinkagecharacteristics. Crystalline or microcrystalline ceramic fibers tend tobe more brittle than amorphous ceramic fibers. Non-intumescent layersmade from crystalline or microcrystalline ceramic fibers can break moreeasily than insulation prepared from amorphous fibers. On the otherhand, crystalline or microcrystalline ceramic fibers tend to have alower bulk shrinkage than amorphous ceramic fibers.

The average diameter of the inorganic fibers is typically at least 3micrometers, at least 4 micrometers, at least 5 micrometers, at least 6micrometers, or at least 7 micrometers. The inorganic fibers usuallyhave an average diameter that is no greater than 20 micrometers, nogreater than 18 micrometers, no greater than 16 micrometers, or nogreater than 14 micrometers. In some embodiments, at least 60 weightpercent of the inorganic fibers have an average diameter that is within3 micrometers of the average diameter. For example, at least 70 weightpercent, at least 80 weight percent, or at least 90 weight percent ofthe inorganic fibers have an average diameter that is within 3micrometers of the average diameter.

The non-intumescent layer(s) or strip(s) can further contain an organicbinder in amounts up to 20 weight percent based on the weight of thenon-intumescent layer. In some embodiments, the organic binder ispresent in amounts up to 10 weight percent, up to 5 weight percent, orup to 3 weight percent based on the weight of the non-intumescent layeror strip. The organic binder is typically burned off when the multilayermat containing the non-intumescent layer or strip is used at elevatedtemperatures such as those typically encountered in a pollution controldevice.

Suitable organic binder materials can include aqueous polymer emulsions,solvent-based polymers, and solvent free polymers. The aqueous polymeremulsions can include organic binder polymers and elastomers in the formof a latex (e.g., natural rubber lattices, styrene-butadiene lattices,butadiene-acrylonitrile lattices, and lattices of acrylate andmethacrylate polymers or copolymers). The solvent-based polymeric bindermaterials can include a polymer such as an acrylic, a polyurethane, avinyl acetate, a cellulose, or a rubber based organic polymer. Thesolvent free polymers can include natural rubber, styrene-butadienerubber, and other elastomers.

In some embodiments, the organic binder material includes an aqueousacrylic emulsion. Acrylic emulsions advantageously tend to have goodaging properties and non-corrosive combustion products. Suitable acrylicemulsions can include, but are not limited to, commercially availableproducts such as those sold under the trade designation “RHOPLEX TR-934”(an aqueous acrylic emulsion having 44.5 weight percent solids) and“RHOPLEX HA-8” (an aqueous emulsion of acrylic copolymers having 45.5weight percent solids) from Rohm and Hass (Philadelphia, Pa.); under thetrade designation “NEOCRYL XA-2022” (an aqueous dispersion of an acrylicresins having 60.5 percent solids) available from ICI Resins US(Wilmington, Mass.); and under the trade designation “AIRFLEX 600BP DEV”(an aqueous emulsion of ethylene vinyl acrylate terpolymer having 55weight percent solids) from Air Products and Chemical, Inc.(Philadelphia, Pa.).

Organic binders can also include a plasticizer, a tackifier, or acombination thereof. Plasticizers tend to soften a polymer matrix andcan enhance the flexibility and moldability of the non-intumescentlayer. For example, the organic binder can include a plasticizer such asisodecyl diphenyl diphosphate commercially available under the tradedesignation “SANTICIZER 148” from Monsanto (St. Louis, Mo.). Tackifiersor tackifying resins can aid in holding the insulation materialtogether. An example of a suitable tackifier is commercially availablefrom Eka Nobel, Inc. (Toronto, Canada) under the trade designation“SNOWTACK 810A”.

The non-intumescent layer(s) or strip(s) can also contain othermaterials such as, but not limited to, plasticizers, wetting agents,dispersants, defoaming agents, latex coagulants, and fungicides. Fillermaterials such as glass particles, calcium carbonate, expandedvermiculite, delaminated vermiculite, mica, perlite, aluminumtrihydrate, magnesium phosphate hexahydrate, zinc borate, and magnesiumhydroxide can be added. Additionally, inorganic binders such as clays,bentonite, and colloidal silica can be added.

The non-intumescent layer(s) or strip(s) can also contain organic fiberssuch as, for example, acrylics, cellulose, polyolefin, polyvinylalcohol, polyester, or combinations thereof. The fibers can be staplefibers or fibrillated fibers. Useful stable fibers typically have a sizeof about 0.5 to 5 denier. Suitable rayon fibers having a size of 1.5denier per filament are commercially available from Minifiber, Inc.(Johnson City, Tex.). Suitable polyvinyl alcohol fibers are commerciallyavailable from Kuraray Americas, Inc. (New York, N.Y.) under the tradedesignation “KURALON”. An acrylic fiber pulp is commercially availableunder the trade designation “CFF” from Cytek Industries, Inc. (WestPaterson, N.J.).

A suitable non-intumescent layer or strip can include, at least in someembodiments, inorganic fibers in an amount of 10 to 99.5 weight percentand organic binders in an amount of 0.5 to 20 weight percent. Forexample, the non-intumescent layer or strip can contain inorganic fibersin an amount of 20 to 99.5 weight percent, organic binder in an amountof 0.5 to 20 weight percent, and up to 60 weight percent inorganicbinders or fillers.

One non-intumescent layer that can be used according to the presentinvention contains heat-treated aluminosilicate ceramic fibers iscommercially available from 3M Company (St. Paul, Minn.) under the tradedesignation “INTERAM 900HT”. This mat has a bulk density of about 0.25g/cm³ and a weight per unit area of about 1020 to about 2455 g/m². Othermore resilient non-intumescent layer(s) or strip(s) include thosecommercially available from 3M Company under the trade designation“INTERAM 1100HT” and “INTERAM 1101HT”. These mats have a bulk density ofabout 0.15 g/cm³ and a weight per unit area of about 440 to about 2100g/m². These mats contain crystalline alumina fibers (i.e.,polycrystalline alumina fibers). Another suitable non-intumescent layerthat includes magnesium aluminosilicate glass fibers is commerciallyavailable from 3M Company under the trade designation “INPE 571.02.”This mat has a bulk density of 0.12 g/cm³ and a weight per unit area ofabout 600 to about 1400 g/m². A needle-bonded mat is commerciallyavailable from Mitsubishi Chemical Company, Tokyo, Japan under the tradedesignation “MAFTEC MLS-3” with a bulk density of about 0.16 g/cm³. Thismat contains about 72 weight percent Al₂O₃ and about 28 weight percentSiO₂ based on the weight of the fibers.

The intumescent layers contains at least one type of intumescentmaterial. The intumescent layers can further include inorganic fibers,organic binders, plasticizers, wetting agents, dispersants, defoamingagents, latex coagulants, fungicides, filler materials, inorganicbinders, and organic fibers. These additional components are the same asthose discussed above for the non-intumescent layer.

Examples of suitable intumescent materials for the intumescent layerinclude unexpanded vermiculite, hydrobiotite, water swellable synthetictetrasilicic fluorine type mica as described in U.S. Pat. No. 3,001,571(Hatch), alkali metal silicate granules as described in U.S. Pat. No.4,521,333 (Graham et al.), expandable graphite, or combinations thereof.Alkaline metal silicate granules are commercially available from 3MCompany (St. Paul, Minn.) under the trade designation “EXPANTROL 4BW”.Expandable graphite is commercially available under the tradedesignation “GRAFOIL GRADE 338-50” from UCAR Carbon Co., Inc.(Cleveland, Ohio). Unexpanded vermiculite is commercially available fromCometals Inc. (New York, N.Y.). In some applications, the intumescentmaterials are selected from unexpanded vermiculite, expandable graphite,or a combination thereof.

The vermiculite can be treated, for example, with salts such as ammoniumdihydrogen phosphate, ammonium nitrate, ammonium chloride, potassiumchloride, or other soluble salts known in the art. The treatment isbased on an ion exchange reaction. The intumescent layer often containat least 5, at least 10, at least 20, at least 40, or at least 60 weightpercent intumescent material based on the weight of the intumescentlayer. In some intumescent layers, the layer can be free of inorganicfibers. In other intumescent layers, the layer can be free of inorganicfibers and organic binders. In still other intumescent layers, the layercontains 5 to about 85 weight percent intumescent material and less than20 weight percent organic binder based on the weight of the intumescentlayer. Inorganic fibers are included in some intumescent layers.

In some more specific example, the intumescent layer includesintumescent materials in an amount of 5 to 85 weight percent, organicbinder in an amount of 0.5 to 15 weight percent, and inorganic fibers inan amount of 10 to 60 weight percent based on the weight of theintumescent layer. In other examples, the intumescent layer includesintumescent materials in an amount of 5 to 70 weight percent, organicbinder in an amount of 0.5 to 10 percent, and inorganic fibers in anamount of 30 to 45 weight percent based on the weight of the intumescentlayer. In still other examples, the intumescent layer includesintumescent materials in an amount of 20 to 65 weight percent, organicbinders in an amount of 0.5 to 20 weight percent, inorganic fibers in anamount of 10 to 65 weight percent, and up to 40 weight percent inorganicfillers or inorganic binders.

Suitable intumescent layers are commercially available from 3M (St.Paul, Minn.) under the trade designations “INTERAM 100”, “INTERAM 200”,“INTERAM 550”, and “INTERAM 2000 LT”. These mats usually have a bulkdensity of about 0.4 to about 0.7 g/cm³ and a weight per unit area ofabout 1050 g/m² to about 8140 g/m². Another suitable intumescent layeris commercially available from 3M under the trade designation “INTERAM570NC”. This layer usually has a weight per unit area of about 1050 g/m²to about 4070 g/m² and contains inorganic fibers that that meet Europeannon-classified fiber regulations.

In some intumescent layers, biosoluble inorganic fibers are included.Intumescent layers containing biosoluble fibers are further described inInternational Patent Application Publication WO 03/031368 (Howorth),incorporated herein by reference in its entirety. As used herein,“biosoluble inorganic fibers” refer to inorganic fibers that aredecomposable in a physiological medium or a simulated physiologicalmedium. Physiological medium refers to, but is not limited to, thosebodily fluids typically found in the respiratory tract such as, forexample, the lungs of animals or humans.

The biosoluble inorganic fibers typically include inorganic oxides suchas, for example, Na₂O, K₂O, CaO, MgO, P₂O₅, Li₂O, and BaO, orcombinations thereof with silica. Other metal oxides or other ceramicconstituents can be included in the biosoluble inorganic fibers eventhough these constituents, by themselves, lack the desired solubilitybut are present in low enough quantities such that the fibers, as awhole, are still decomposable in a physiological medium. Such metaloxides include, for example, Al₂O₃, TiO₂, ZrO₂, B₂O₃, and iron oxides.The biosoluble inorganic fibers can also include metallic components inamounts such that the fibers are decomposable in a physiological mediumor simulated physiological medium.

In one embodiment, the biosoluble inorganic fibers include silica,magnesium oxide, and calcium oxide. These types of fibers are typicallyreferred to as calcium magnesium silicate fibers. The calcium magnesiumsilicate fibers usually contain less than about 10 weight percentaluminum oxide. Suitable biosoluble fibers can include 45 to 90 weightpercent SiO₂, up to 45 weight percent CaO, up to 35 weight percent MgO,and less than 10 weight percent Al₂O₃. For example, the fibers cancontain about 55 to about 75 weight percent SiO₂, about 25 to about 45weight percent CaO, about 1 to about 10 weight percent MgO, and lessthan about 5 weight percent Al₂O₃.

Exemplary biosoluble inorganic oxides fibers are described in U.S. Pat.Nos. 5,332,699 (Olds et al.); 5,585,312 (TenEyck et al.); 5,714,421(Olds et al.); and 5,874,375 (Zoitas et al.). Various methods can beused to form biosoluble inorganic fibers including, but not limited to,sol gel formation, crystal growing processes, and melt formingtechniques such as spinning or blowing.

Biosoluble fibers are commercially available from Unifrax Corporation(Niagara Falls, N.Y.) under the trade designation “INSULFRAX”. Otherbiosoluble fibers are sold by Thermal Ceramics (located in Augusta, Ga.)under the trade designation “SUPERWOOL.” For example, SUPERWOOL 607contains 60 to 70 weight percent SiO₂, 25 to 35 weight percent CaO, 4 to7 weight percent MgO, and a trace amount of Al₂O₃. SUPERWOOL 607 MAX canbe used at a slightly higher temperature and contains 60 to 70 weightpercent SiO₂, 16 to 22 weight percent CaO, 12 to 19 weight percent MgO,and a trace amount of Al₂O₃.

An exemplary intumescent layer can include intumescent material in anamount of 10 to 80 weight percent, biosoluble inorganic fibers in anamount of 5 to 80 weight percent, micaceous binder in an amount of 5 to80 weight percent, and organic binder in an amount of 0.5 to 20 weightpercent.

As used herein, “micaceous binder” refers to one or more micaceousminerals that can be wetted and then dried to form a cohesive body thatis self-supporting. As used herein, “self-supporting” refers to amicaceous binder that can be formed into a 5 cm×5 cm×3 mm sheetcontaining no other materials such that the dried sheet can be heldhorizontally at any edge for at least 5 minutes at 25° C. and up to 50percent relative humidity without crumbling or otherwise falling apart.

As used herein, the phrase “micaceous mineral” refers to a family ofminerals that can be split or otherwise separated into planar sheets orplatelets. Micaceous minerals include, but are not limited to, expandedvermiculite, unexpanded vermiculite, and mica. Micaceous mineralstypically have an average aspect ratio (i.e., the length of a particledivided by its thickness) that is greater than about 3. Micaceousminerals that typically have a particle size less than about 150micrometers (e.g., the micaceous binder contains micaceous minerals thatcan pass through a 100 mesh screen). In some embodiments, the micaceousbinder contains micaceous minerals having a size less than about 150micrometers and having an average aspect ratio of greater than about 8or greater than about 10.

Suitable micaceous binders can include micaceous minerals that have beencrushed. As used herein, “crushed” refers to micaceous minerals thathave been processed in any suitable manner that reduces the averageparticle size. Methods of crushing include, but are not limited to,mechanical shearing of a dilute or concentrated slurry, milling, airimpact, and rolling. Other methods can be used alone or in combinationwith crushing to reduce the particle size. For example, thermal orchemical methods can be used to expand or expand plus exfoliate themicaceous minerals. Expanded vermiculite can be sheared or otherwiseprocessed in water to produce an aqueous dispersion of delaminatedvermiculite particles or platelets. Shearing can be adequatelyperformed, for example, using a high shear mixer such as a blender.

In some embodiments, the micaceous binder includes processedvermiculites (i.e., vermiculate that has been expanded, delaminated, andcrushed). Processed vermiculite is typically non-intumescent. In otherembodiments, the micaceous binder includes vermiculite that has not beenexpanded and delaminated or that has been only partially expanded anddelaminated. Such materials tend to be intumescent.

Suitable micaceous binders are commercially available from W. R. Grace &Company, and include a delaminated vermiculite powder (under the tradedesignation “VFPS”) and an aqueous dispersion of chemically exfoliatedvermiculite (under the trade designation “MICROLITE). Also, expandedvermiculite flakes are available from W.R. Grace and Company (under thetrade designation “ZONELITE #5”) that can be reduced in particle size toform a micaceous binder.

The micaceous binder can include vermiculite having a particle size lessthan about 150 micrometers and the intumescent material can includevermiculite having a particle size greater than about 150 micrometers(none passes through a 100 mesh screen). The intumescent vermiculite canhave an average particle size that is greater than about 300micrometers.

In one embodiment of a multilayer mat, the non-intumescent layer(s) orstrip(s) contains glass fibers and the intumescent layer(s) containvermiculite. In another embodiment of the multilayer mat, thenon-intumescent layer(s) or strip(s) contains refractory ceramic fibershaving a shrinkage no greater than 10 percent based on the TMA test andthe intumescent layer(s) contain vermiculite.

Each non-intumescent layer or strip in the multilayer mat usually has abulk density in the range of about 0.05 g/cm³ to about 0.4 g/cm³ whilethe intumescent layer has a bulk density in the range of about 0.4 g/cm³to about 0.75 g/cm³. As used herein, the term “bulk density” refers tothe density of a layer, strip or multilayer mat that is not undercompression. The bulk density of the multilayer mat depends on thethickness and composition of the various layers but is typically about0.2 g/cm³ to about 0.5 g/cm³. In some applications, the multilayer matshave a compressed density of about 0.4 g/cm³ to about 0.9 g/cm³. As usedherein, the term “compressed density” refers to the density of themultilayer mat after being assembled around a pollution control elementin a pollution control device. A paper making process is used to formthe non-intumescent layer(s), strip(s), the intumescent layer(s), or acombination thereof. For example, a non-intumescent layer(s) or strip(s)can be prepared by forming an aqueous slurry containing the inorganicfibers. The aqueous slurry often contains up to 30 weight percent solidsbased on the weight of the slurry (e.g., the slurry can contain up to 20weight percent or up to 10 weight percent solids based on the weight ofthe slurry). The slurry often contains at least 1 percent solids basedon the weight of the slurry (e.g., slurry can contain at least 2 weightpercent or at least 3 weight percent solids). In some embodiments, theslurry can contain 1 to 10, 2 to 8, or 3 to 6 weight percent solids.Higher solids can be advantageous because less water needs to be removedto prepare the preform. However, slurries with higher percent solidstend to be more difficult to mix.

The intumescent layer can be prepared by forming an aqueous slurrycontaining the intumescent material. The percent solids can becomparable to those used to prepare the non-intumescent layer. Theaqueous slurry for the intumescent layer often contains inorganic fibershowever intumescent layers can be free of inorganic fibers.

The water used in each aqueous slurry can be well water, surface water,or water that has been treated to remove impurities such as salts andorganic compounds. When well or surface water is used in the aqueousslurry, salts (e.g., calcium and magnesium salts) present in the watercan function as an inorganic binder. In some embodiments, the water isdeionized water, distilled water, or a combination thereof.

Other additives can also be included in each aqueous slurry composition.Such additives can include inorganic binders, inorganic fillers,defoamers, flocculants, surfactants, and the like. Strength enhancingagents can also be included such as, for example, organic fibers.

Other methods can be used to prepare the non-intumescent layer(s) orstrip(s). In some applications, the non-intumescent layer or strip canbe prepared as a non-woven mat by chopping individual inorganic fibersto a desired length. Such a method is described in International PatentApplication Publication WO 2004/011785 (Merry et al.), incorporatedherein by reference. The individualized fibers can be prepared bychopping a tow or yarn of fiber using a glass roving cutter commerciallyavailable under the trade designation “MODEL 90 GLASS ROVING CUTTER”from Finn and Fram, Inc. (Pacoma, Calif.). Alternatively, the choppedindividualized fibers can be formed using a hammer mill and then ablower. The fibers are usually chopped to a length ranging from about0.5 to about 15 cm. A mat can be formed using a conventional web formingmachine such as those commercially available from Rando Machine Corp.(Macedon, N.Y.) under the trade designation “RANDO WEBBER” or fromScanWeb Co. (Denmark) under the trade designation “DAN WEB”. The choppedindividualized fibers can be drawn onto a wire screen or mesh belt(e.g., a metal or nylon belt). Depending on the length of the fibers,the resulting mat can have sufficient handleability to be transferred toa needle punch or stitch bonding machine without a support such as ascrim. To facilitate ease of handing, some mats can be formed or placedon a scrim.

A needle-punched nonwoven mat refers to a mat where there is physicalentanglement of the inorganic fibers provided by multiple full orpartial penetrations of the mat with barbed needles. Needle punchinggenerally involves compressing a nonwoven mat and then punching anddrawing barbed needles through the mat. Although the optimum number ofneedle punches per area of mat depends on the particular application,the nonwoven mat is often punched to provide about 5 to about 60punches/cm². In some applications the mats have 10 to about 20punches/cm². The nonwoven mat can be needle punched using a conventionalneedle punching machine such as those commercially available from Dilo(Germany) with barbed needles commercially available from Foster NeedleCompany (Manitowoc, Wis.).

Alternatively, the nonwoven mat can be stitch bonded using techniquessuch as those disclosed in U.S. Pat. No. 4,181,514 (Lefkowitz et al.),the disclosure of which is incorporated herein by reference. The mat canbe stitch bonded using an organic thread or an inorganic thread (e.g.,ceramic or stainless steel). A relatively thin layer of inorganic ororganic sheet material can be placed on either or both sides of the matduring stitching to prevent or minimize the threads from cutting throughthe mat. The spacing of the stitches can be varied but is usually about3 to about 30 mm so that the fibers are uniformly compressed throughoutthe entire area of the mat. A commercially available needle punchednon-intumescent layer can be obtained from Mitsubishi Chemical (Tokyo,Japan) under the trade designation “MAFTEC”.

The intumescent layer can be in the form of a paste applied to a majorsurface of a non-intumescent layer. Suitable paste compositions forintumescent layers are further described, for example, in U.S. Pat. No.5,853,675 (Howorth) and U.S. Pat. No. 5,207,989 (MacNeil), incorporatedherein by reference. Some of these compositions include inorganic fibersin addition to the intumescent material. The pastes can be appliedinitially, for example, to a substrate such as a release liner or paper.The substrate can be removed after contacting the paste with a majorsurface of a non-intumescent layer.

In other multilayer mats, the intumescent layer can be formed byspraying a suitable intumescent composition onto a major surface of anon-intumescent layer. The compositions can include, for example, othermaterials such as inorganic fibers or organic binders. Alternatively,intumescent material free of a binder can be applied to a portion of amajor surface of a non-intumescent layer.

The various layers can be individually prepared and then bondedtogether. The various layers of the multilayer mat can be bonded to eachother using needle punching or stitch bonding techniques. Some of themultilayer mats have an adhesive to adhere the non-intumescent andintumescent layers together. Each layer can be prepared separately andthen bonded together. The adhesive can be a pressure sensitive adhesiveor a hot melt adhesive. In some multilayer mats, the adhesive is a hotmelt adhesive such as, for example, the adhesive commercially availablefrom Bostik-Findley (Stafford, UK) under the trade designation “PE105-50” or “PE 65-50”.

The multilayer mat can be prepared using a paper making process. Onesuch process is described in U.S. Patent Publication 2001/0046456(Langer et al.), the disclosure of which is incorporated herein byreference. A first slurry containing inorganic fibers can be preparedand then deposited on a permeable substrate. The deposited first slurrycan be partially dewatered to form a first layer. An intumescentcomposition can be applied to a portion of the first layer to form asecond layer. The intumescent composition can be applied, for example,by spraying if the composition includes a liquid or by sprinkling if thecomposition is free of a liquid. A second slurry containing inorganicfibers can be prepared and then deposited on over the second layer andany exposed first layer. The deposited third slurry can be at leastpartially dewatered to form a third layer. After the final layer hasbeen deposited, the mat can be dried to remove at least a portion of anyremaining water. For example, the mat can be compressed and dried bypassing the mat through heated rollers

Such a process can result in some intermingling of the layers. Theintermingling of the layers can be practically invisible to the eye orcan be to such an extent that a visible boundary or gradient layer formsbetween two adjacent layers. With such a process, the layers can bebonded together without the use of an adhesive, stitches, needles, orstaples.

The foregoing describes the invention in terms of embodiments foreseenby the inventor for which an enabling description was available,notwithstanding that insubstantial modifications of the invention, notpresently foreseen, may nonetheless represent equivalents thereto.

1. A multilayer mat for mounting a pollution control element in apollution control device, said mat comprising: a.) at least one firstlayer having an exposed major surface, a length, and a width defined byopposite lateral edges, with the length of said first layer beinggreater than the width of said first layer, and at least one lateraledge of said first layer requiring protection from exposure to at leastone of (i) mechanical erosion forces generated by the impact of exhaustgases passing through the pollution control device and (ii) hightemperatures associated with the exhaust gases passing through thepollution control device, where the exhaust gases contact the at leastone lateral edge of said first layer, when said multilayer mat mounts apollution control element in a pollution control device; and b.) atleast one second layer having a length, and a width defined by oppositelateral edges that is larger than the width of said first layer, with atleast one lateral edge of said second layer being sufficiently resilientand durable to withstand exposure to at least one of (i) mechanicalerosion forces generated by the impact of the same exhaust gases as ina.)(i) and (ii) high temperatures associated with the same exhaust gasesas in a.)(ii), wherein said first layer and said second layer arestacked one on top of the other, with no portion of said second layerbeing coplanar with said first layer and said at least one lateral edgeof said first layer being positioned between the opposite lateral edgesof said second layer such that, when said multilayer mat is mounted inthe pollution control device, the at least one lateral edge of saidsecond layer will shield the at least one lateral edge of said firstlayer from exposure to exhaust gases passing through the pollutioncontrol device.
 2. The multilayer mat as in claim 1, wherein bothlateral edges of said first layer are positioned between the oppositelateral edges of said second layer such that, when said multilayer matis mounted in the pollution control device, both lateral edges of saidfirst layer are protected from exposure to exhaust gases passing throughthe pollution control device.
 3. The multilayer mat as in claim 1,wherein said at least one first layer and said at least one second layereach comprises a non-intumescent layer or an intumescent layer.
 4. Themultilayer mat as in claim 1, wherein said at least one first layer is anon-intumescent layer and said at least one second layer is anintumescent layer, or said at least one first layer is an intumescentlayer and said at least one second layer is a non-intumescent layer. 5.The multilayer mat as in claim 1, wherein said at least one first layerand said at least one second layer are disposed relative to one anothersuch that both lateral edges of said at least one first layer arepositioned within the lateral edges of said at least one second layer.6. The multilayer mat as in claim 1, wherein said at least one firstlayer and said at least one second layer are disposed relative to oneanother such that one of the lateral edges of said at least one firstlayer is in-line with one of the lateral edges of said at least onesecond layer, and only the other lateral edge of said at least one firstlayer lies within the lateral edges of said at least one second layer.7. The multilayer mat as in claim 1, further comprising a strip of oneor more layers positioned alongside one lateral edge of said at leastone first layer, wherein the combined widths of said strip and saidfirst layer are together substantially equal to or less than the widthof said second layer.
 8. The multilayer mat as in claim 7, furthercomprising two strips of one or more layers each, with one said stripbeing disposed alongside each lateral edge of said at least one firstlayer, wherein the combined widths of both said strips and said firstlayer are together substantially equal to the width of said secondlayer.
 9. The multilayer mat as in claim 7, wherein each said strip andsaid at least one first layer are substantially co-planar.
 10. Themultilayer mat as in claim 7, wherein each said strip is more resilientthan said second layer.
 11. The multilayer mat as in claim 7, whereinsaid second layer is more resilient than any said strip.
 12. A pollutioncontrol device comprising: a housing having an inner wall; a pollutioncontrol element disposed in said housing so as to form a gaptherebetween; and a multilayer mat as in claim 1, wherein said mat isdisposed in said gap so as to mount said pollution control element insaid housing.
 13. The pollution control device as in claim 12, wherein aportion of the inner wall of said housing defines a recess, and said matis positioned so that at least a portion of only said first layer isreceived within said recess.
 14. The pollution control device as inclaim 12, wherein a portion of the inner wall of said housing defines arecess, said mat is positioned so that at least a portion of said firstlayer is received within said recess, and neither lateral edge of saidfirst layer is exposed to exhaust gases passing through said pollutioncontrol device.
 15. The pollution control device as in claim 12, whereina portion of the inner wall of said housing defines a recess, said matis positioned so that said first layer is received within said recess,and one or no lateral edge of said first layer is exposed to exhaustgases passing through said pollution control device.
 16. The pollutioncontrol device as in claim 12, wherein said multilayer mat furthercomprises a strip of one or more layers positioned alongside one lateraledge of said at least one first layer, the combined widths of said stripand said first layer are together substantially equal to or less thanthe width of said second layer, a portion of the inner wall of saidhousing defines a recess, said mat is positioned so that said firstlayer is received within said recess and not exposed to exhaust gasespassing through said pollution control device, and one said strip isexposed to exhaust gases passing through said pollution control device.17. The pollution control device as in claim 12, wherein said secondlayer is positioned adjacent said pollution control element, and saidfirst layer is positioned adjacent the inner wall of said housing. 18.The pollution control device as in claim 12, wherein at least one of thelateral edges of said first layer is substantially sealed from exposureto exhaust gases passing through said pollution control device.
 19. Thepollution control device as in claim 12, wherein said device is acatalytic converter or an exhaust system filter.
 20. A pollution controldevice comprising: a housing having an inlet and an outlet, throughwhich exhaust gases flow into and out of said pollution control device,and an inner wall; a pollution control element disposed in said housingso as to form a gap therebetween; and a multilayer mat disposed in saidgap so as to mount said pollution control element in said housing, saidmat comprising: at least one first layer having a first width defined byopposite first lateral edges and a major surface that faces either saidinner wall of said housing or said pollution control element, with atleast one first lateral edge of said first layer needing protection fromexposure to at least one of (i) mechanical erosion forces generated bythe impact of the exhaust gases on said at least one first lateral edgeand (ii) high temperatures associated with the exhaust gases; and atleast one second layer having a second width defined by opposite secondlateral edges, and said second width being larger than said first width,with at least one second lateral edge of said second layer beingsufficiently resilient and durable to withstand exposure to at least oneof (i) mechanical erosion forces generated by the impact of the exhaustgases on said at least one second lateral edge and (ii) hightemperatures associated with the exhaust gases, wherein said first layerand said second layer are stacked one on top of the other and disposedin said housing, with no portion of said second layer being coplanarwith said first layer and said at least one first lateral edge beingpositioned between the opposite lateral edges of said second layer, suchthat exhaust gases passing through said pollution control device contactsaid at least one second lateral edge and said at least one secondlateral edge protects said at least one first lateral edge from exposureto the exhaust gases passing through said pollution control device.